The Different Forms of Flowers on Plants of the Same Species

m sali

n of the t

plex manner of fert

fferent uni

eminently femi

fferi likewi

folia di

ifolia ho

ticillata

mia, natur

imorphic s

aldi

illegitimate un

peci

ensi

d species

cotyledonous genus known

ec

which present three forms. These have been observed in three families, and consist of species of Lythrum and of the allied genus Nesaea, of Ox

m sali

he flowers of the three fo

ith the petals and calyx

ed six

Long-

: Mid-

Short-

arrows show the directio

stigma to ensure

tional differences are considered, there are five distinct sets of males. Two of the three hermaphrodites must coexist, and pollen must be carried by insects reciprocally from one to the other, in order that either of the two should be fully fertile; but unless all three forms coexist, two sets of stamens will be wasted, and the organisation of the species, as a whole, will be incomplete. On the other hand, when all three hermaphro

ms was first observed by Vaucher, and subsequently more carefully by Wirtgen ; but these botanists, not being guided by any theory or even suspicion of their functional differences, did not perceive some of the most curious points of difference in their structure. (4/1. Vaucher 'Hist. Phys. des Plantes d'Europe' tome 2 1841 page 3

STYLE

f the mid-styled form. Such correspondence in this and the two following forms is generally very close; the difference, where there is any, being usually in a slight excess of length in the stamens. The six shortest stamens lie concealed within the calyx; their ends are turned up, and they are graduated in length, so as to form a double row. The anthers of these stamens are smaller than those of the mid-length ones. The pollen is of the same yellow colour in both sets. H. Muller measured the pollen-grain in all three forms, and his measurements are evidently more trustworthy than those which I formerly made, so I will give them. (4/2. 'Die Befruchtung der Blumen' 1873 page 193.) The

TYLED

rly dehiscence they appear emerald-green. Hence in general appearance these stamens are remarkably dissimilar from the mid-length stamens of the long-styled form. The six shortest stamens are enclosed within the calyx, and resemble in all respects the shortest stamens of the long-styled form; both these sets correspond in length with the short pistil of the short-styled form. The green pollen-grains of the longest stamens a

STYLED

But according to H. Muller, their pollen-grains are a little larger, namely 9 1/2 to 10 1/2, instead of 9 to 10 in diameter. The six mid-length stamens, with their uncoloured filaments and yellow pollen, resemble in the size of their pollen-grains and in all other respects the corresponding stamens of the long-styled form. The difference in diameter between the grains from the two sets of anthers in

another in length, curvature, and colour of the filaments-in the size of the anthers, and especially in the colour and diameter of the pollen-grains. Each form bears half-a-dozen of one kind of stamens and half-a-dozen of another kind, but not all three kinds. The three kinds of stamens correspond in length with the

a. Diameters of pollen-grai

ource of Po

Minimum

Maximum

short-styled form

s of mid-style

s of long-styled

s of short-styled

of long-styled

ns of mid-styl

est stamens, and the least (smallest) from the shortest; the

me between the three forms gave, as may be seen in the following tables, for the long- styled an average of 90 seeds, for the mid-styled 117, and for the short-styled 71. So that we have good concurrent evidence of a difference in the average production of seed by the three forms. To show that the unions effected by me often produced their full effect and may be trusted, I may state that one mid- styled capsule yielded 151 good seeds, which is the same number as in the finest wild capsule which I examined. Some artificially fertilised short- and long- styled capsules produced a greater number of seeds than was ever observed by me in wild plants of the same forms, but then I did not examine man

ends gathered for me in North Wales a number of twigs from separate plants growing near on

caria. Classification ac

: Place

2: Long

3: Mid-

4: Shor

n 5:

: 95 : 97

: 53 : 38

8 : 135 :

if he had collected in another spot, he felt sure that the mid-styled plants would have been in excess. I several times sowed small parcels of seed, and raised all three forms; but I neglected

hers, and the ends of the pistils with their stigmas, are a little upturned, so that they may be brushed by the lower hairy surfaces of the insects' bodies. The shortest stamens which lie enclosed within the calyx of the long- and mid-styled forms can be touched only by the proboscis and narrow chin of a bee; hence they have their ends more upturned, and they are graduated in length, so as to fall into a narrow file, sure to be raked by the thin intruding proboscis. The anthers of the longer stamens stand laterally farther apart and are more nearly on the same level, for they have to brush against the whole breadth of the insect's body. In very many other flowers the pistil, or the stamens, or both, are rectangularly bent to one side of the flower. This bending may be permanent, as with Lythrum and many others, or may be effected, as in Dictamnus fraxinella and others, by a temporary movement, which occurs in the case of the stamens when the anthers dehisce, and in the case of the pistil when the stigma is mature; but these two movements do not always take place simultaneously in the same flower. Now I have found no exception to the rule, that when the stamens and pistil are bent, they bend to that side of the flower which secretes nectar, even though there be a rudimentary

flower. On catching bees, I observed much green pollen on the inner sides of the hind legs and on the abdomen, and much yellow pollen on the under side of the thorax. There was also pollen on the chin, and, it may be presumed, on the proboscis, but this was difficult to observe. I had, however, independent proof that pollen is carried on the proboscis; for a small branch of a protected short-styled plant (which produced spontaneously only two capsules) was accidentally left during several days pressing against the net, and bees were seen inserting their proboscides through the meshes, and in consequence numerous capsules were formed on this one small branch. From these several facts it follows that insects will genera

right angles. The stigma of the long-styled pistil frequently has longer papillae or is rougher than that of the mid-styled, and the latter than that of the short-styled; but this character, though fixed and uniform in the two forms of Primula veris, etc., is here variable, for I have seen mid- styled stigmas rougher than those of the long-styled. (4/5. The plants which I observed grew in my garden, and probably varied rather more than those growing in a state of nature. H. Muller has described the stigmas of all three forms with great care, and he appears to have found the stigmatic papillae differing constantly in length and structure in the three forms, being longest in the long-styled form.) The degr

AL FERTILISATION BET

cient, and that it was necessary to try all six kinds of pollen on each stigma. As in fertilising flowers there will always be some failures, it would have been advisable to have repeated each of the eighteen unions a score of times; but the labour would have been too great; as it was, I made 223 unions, i.e. on an average I fertilised above a dozen flowers in the eighteen different methods. Each flower was castrated; the adjoining buds had to be removed, so that the flowers might be safely marked with thread, wool, etc.; and after each fertilisation the stigma was examined with a lens to see that there was sufficient pollen on it. Plants of all three forms were protected during two years by

sult of the application of each form's own two kinds of pollen from the two sets of stamens belonging to the same form, and which do not equal the pistil in length. These unions are likewise illegitimate. The term own-form pollen here used does not mean pollen from the flower to be fertilised-for this was never used-but from another flower on the same plant, or more commonly from a distinct plant of the same form. The figure "0" means that no capsule was produced, or if a capsule was produced that it contained no good seed. In some part of each row of figures in each compartment, a short horizontal line may be seen; the unions above this line were made in 1862, and below it in 1863. It

rum salicaria, l

.1. Legiti

ens of the mid-styled. These stamens equa

ood seed in

6

1

ded capsules. Each capsule conta

.2. Legiti

ns of the short-styled. These stamens equa

ood seed in

9

1

or se

3

1

ded capsules. Each capsule conta

3. Illegiti

by the shortest stam

0 0 0 0

le for an

4. Illegiti

by the mid-length stam

0 0 0 0

le for an

5. Illegiti

ised by own-form

0

3

le for an

6. Illegiti

ised by own-form

0 0 0 0 0

le for an

I tried a much better experiment: a long-styled plant was grown by itself, miles away from any other plant, so that the flowers could have received only their own two kinds of pollen. The flowers were incessantly visited by bees, and their stigmas must have received successive app

0 35

4 12

27

2 29

m, fertilised by its own two pollens, yields only between one-fourth and one-fifth of the full number of seed. I have spoken as if the plant had received both its own kinds of pollen, and this is, of course, possible; but, from

hrum salicaria,

.1. Legiti

amens of the long-styled. These stamens eq

ood seed in

147 151 109 119

0 per cent) yielded capsules. Each capsu

.2. Legiti

amens of the short-styled. These stamens e

ood seed in

2

0

3

0

3

0

e contained, on an average, 108.0 seeds; or, excluding cap

3. Illegiti

by the shortest stam

3

ds small

4

4

5

e contained, on an average, 47.4 seeds; or, excluding cap

4. Illegiti

by the longest stame

0

5

4

3

e contained, on an average, 69.5 seeds; or, excluding cap

5. Illegiti

lised by own-for

2

3

6?

dly any doubt that I fertilised a flower marked with "white thread" as if it had been marked with "white silk." With respect to the capsule which yielded 92 seeds, in the same column with that which yielded 136, I do not know what to think. I endeavoured to prevent pollen dropping from an upper to a lower flower, and I tried to remember to wipe the pincers carefully after each fertilisation; but in making eighteen different unions, sometimes on windy days,

ded capsules, and each capsule contained, on an average, 54.6 seeds;

6. Illegiti

ised by own-form

0 0 - 0

wer yielded

ers with pollen, taken by a camel's-hair brush, from both the longest and shortest stamens o

rum salicaria, s

.1. Legiti

ens of the long-styled. These stamens equa

9

1

1

1

ed capsules. Each capsule conta

.2. Legiti

ens of the mid-styled. These stamens equal

3

7

8

3

ed capsules. Each capsule conta

3. Illegiti

by the mid-length stam

le for an

. 10 flowers fertilised by the l

0 0 0

le for an

5. Illegiti

lised by own-for

0 0 -

le for an

6. Illegiti

ised by own-form

?*

1

ng-styled form, and it would then have yielded about 64 seeds. Flowers to be thus fertilised were marked with black silk;

le for an

er of flowers without particular care with their own two

OF THE

STYLE

sponding length, borne by the mid-and short-styled forms, yielded

imately by the other stamens of the mid-and short

yielded only eight very poor capsules; but long-styled flowers fertilised by bees with po

TYLED

borne by the long and short-styled forms, yielded 96 (probably 100) per cent of caps

of the short-styled form yielded 93 per cent of capsules, which (excluding

th stamens of the long-styled form yielded 54 per cent of capsules, w

n-form longest stamens yielded 25 per cent of capsules, which (

llegitimately by their own-form shorte

STYLED

th, borne by the long and mid-styled forms, yielded 72 per cent of capsules, whi

ately by the other stamens of the long and mid-s

legitimately by their own stamens yielded

ether, and all twelve illegitimate union

LE

: Nature

ber of Flower

mber of Caps

ge Number of Se

Number of Seeds pe

e unions : 75 : 5

mate unions : 146 :

judged by the proportion of the fertilised flowers which yielded capsules, is a

ngest, twelve mid-length, and twelve shortest stamens acts very differently on each of the three stigmas; so that there are three sets of female and of male organs. Moreover, in most cases the six stamens of each set differ somewhat in their fertilising power from the six corresponding ones in one of the other forms. We may further draw the remarkable conclusion that the greater the inequality in length between the pistil and the set of stamens, the pollen of which is employed for its fertilisation, by so much is the sterility of the union increased. There are no exceptions to this rule. To understand what follows the reader should look to Tables 4.23, 4.24 and 4.25, and to the diagram Figure 4.10. In the long-styled form the short stamens obviously differ in length from the pistil to a

hat when from the position of the parts the liability in one form to self- fertilisation is greater than in the other, a union of this kind has been checked by having been rendered the more sterile of the two. But this explanation does not apply to Lythrum; thus the stigma of the long-styled form is more liable to be illegitimately fertilised with pollen from its own mid- length stamens, or with pollen from the mid-length stamens of the short-styled form, than by its own shortest stamens or those of the mid-styled form; yet the two former unions, which it might have been expected would have been guarded aga

ed in the six different possible methods, evinces five grades of fertility. By comparing Tables 4.24.3 and 4.24.6 we may see that the action of the pollen from the shortest stamens of the long-styled and mid-styled forms is widely different; in the one case above half the fertilised flowers yielded capsules containing a fair number of seeds; in the other case not one capsule was produced. So, again, the green, large-grained pollen from the longest stamens of the short-styled and mid-styled forms (in Tables 4.24.4 and 4.24.5) is widely different. In both these cases the difference in action is so plain that it cannot be mistaken, but it can be corroborated. If we look to Table 4.25 to the legitimate action of the shortest stamens of the long- and mid-styled forms on the short-styl

e corresponding stamens of the long- styled are 6 to 6 1/2 in diameter. It would thus appear as if the male organs of the mid-styled form, though not as yet rudimentary, were tending in this direction. On the other hand, the female organs of this form are in an eminently efficient state, for the naturally fertilised capsules yielded a considerably larger average number of seeds than those of the other two forms-almost every flower which was artificially fertilised in a legitimate manner produced a capsule-and most

ame stigma would perhaps yield more seed than one kind by itself; but we have seen that this is not so with each form's own two kinds of pollen; nor is it probable in any case, as I occasionally got, by the use of a single kind of pollen, fully as many seeds as a capsule naturally fertilised ever produces. Moreover the pollen from a single anther is far more than sufficient to fertilise fully a stigma; hence, in this as with so many other plants, more than twelve times as much of each kind of pollen is produced as is necessary to

three females, different in structure and function, and three or even five sets (if minor differences are consider

um Gra

ns rise rather above the middle of the calyx. In the mid-styled form the stigma projects just above the mouth of the calyx, and stands almost on a level with the mid-length stamens of the long and short-styled forms; its own longest stamens project well above the mouth of the calyx, and stand a little above the level of the stigma of the long-styled form. In short, without entering on further details, there is a close general correspondence in structure between this species and L. salicaria, but with some differences in the proportional lengths of the parts. The fact of each of the three pistils hav

m thym

alyx, in the other it was included within the calyx; in this latter form the style was only one-fourth of the length of that in the other form. There are only six stamens; these are somewhat graduated in length, and their anthers in the short-styled form stand a little above the stigma,

hyssop

, which vary in being either present or absent, correspond with the six shorter stamens of L. salicaria and with the six which are always absent in L. thymifolia. The stigma is included within the calyx, and stands in the midst of the anthers, and would generally be fertilised by them; but as the stigma and anthers are upturned, and as, according to Vaucher, there is a passage left in the upper side of the flower to the nectary, there can hardly be a doubt that the flowers are visited by insects, and would occasionally be cross-fertilised by them, as surel

are heterostyled and trimorphic; one apparentl

verti

Graefferi. The green pollen-grains from the longest stamens, measured along their longer axis and not distended with water, were 13/7000 of an inch in length; those from the mid-length stamens 9 to 10/7000, and those from the shortest stamens 8 to 9/7000 of an inch. So that

roemia

f L. reginae, though growing by itself, produced fruit. I examined dried flowers from two plants of L. parviflora, both of which were long-styled, and they differed from L. Indica in having eight long stamens with thick filaments, and a crowd of shorter stamens. Thus the evidence whether L. Indica is heterostyled is curiously conflicting: the unequal number of the short and long stamens, their extreme variability, and especially the fact of their pollen-grains not differing in size, are strongly opposed to this belief; on the other hand, the difference in length of the pistils in two of the plants, their sterility with their own pollen, and the difference in length and structure of the two sets of stamens in the same flower, and in the colour of their pollen, favour the belief. We know that when plants of any kind revert to a former condition, they are apt to be highly variable, and the two halves of the same organ sometimes differ much, as in the case of the above-described anther of the Lagerstroemia; we may therefore suspect that this species was once heterostyled, and that it still retains traces of its former state, together with a tendency to revert more completely to it. It deserves notice, as bearing on the nature of Lagerstroemia, that in Lythrum hyssopifolia, which is a homostyled species, some of the shorter stamens vary in being either present or absent; and that these same stamens are altogether abs

(Gerani

is speciosa (with

Long-s

: Mid-

Short

ed lines with arrows show

for legitimate

ves drawings of the three forms at page 42 of his 'Geschlechter-Vertheilung' etc. 1867.) He also made some interesting observations on living plants belonging to one form alone; for at that time he did not possess the three forms of any living species. During the years 1864 to 1868 I occasionally experimented on Oxalis speciosa, but until now have never found time to publish the results. In 1871 Hildebrand published an admirable paper in which he shows in the case of two species of Oxalis, that the sexual relations of the three forms are nearly the same as in Lythrum salicaria. (4/13. 'Botanische Zeitung' 1871 pages 416 and 432.) I will now give an abstract of his observations, and

Valdi

tes that the stigmas of the three forms do not differ in any marked manner, but that the pistil of t

Diameters of pollen-grains i

ource of Po

Minimum

Maximum

m t

of short-style

ns of short-styl

ns of mid-sty

ens of mid-st

mens of long-s

ens of long-s

or as 100 to 71. The results of Hildebrand's experiments are

is Valdiviana (f

Nature of

ber of Flower

mber of Caps

mber of Seed

st stamens of short-styled. Le

st stamens of mid-styled. Legi

own-form mid-length stamens. Il

nd own-form shortest stamens.

est stamens of short-styled. I

test stamens of mid-styled. I

gth stamens of long-styled. Leg

gth stamens of short-styled. Le

d own-form longest stamens. Il

d own-form shortest stamens. I

est stamens of long-styled. I

t stamens of short-styled. Ill

test stamens of long-styled. L

test stamens of mid-styled. Le

and own-form longest stamens.

nd own-form mid-length stamens.

gest stamens of mid-styled. I

length stamens of long-styled.

erage. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers that yielded capsules, is as 100 to 2, and as judged by the average number of seeds per capsule as 100 to 34. It may be added that some plants

s Reg

, whilst it is very hairy in the other two forms. The diameter of the pollen-grains from both sets of the longest stamens equals 9 divisions of the micrometer,-that from the mid-length stamens of the long- styled form between 8 and 9, and of the short-styled 8

lis Regnelli (f

Nature of

ber of Flower

mber of Caps

ge Number of Se

st stamens of short-styled. Le

est stamens of mid-styled. Le

wn mid-length stamens. Ill

wn shortest stamens. Illeg

ngth stamens of short-styled.

gth stamens of long-styled. Leg

wn longest stamens. Illeg

wn shortest stamens. Ille

st stamens of short-styled. I

rtest stamens of mid-styled.

rtest stamens of long-styled.

wn mid-length stamens. Ille

own longest stamens. Illeg

length stamens of long-styled.

ining on an average 10.31 seeds; whilst 39 flowers fertilised illegitimately did not yield a single capsule or seed. Therefore the fertility of the six legitimate to t

s spe

1) has already been given. The stigma of the long-styled form (with the papillae on its surface included) is twice as large as that of the short-styl

Diameters of pollen-grains i

ource of Po

Minimum

Maximum

m t

of short-styled

s of short-styled

ns of mid-sty

s of mid-styled

mens of long-s

ns of long-sty

measurements were taken at different times, they are probably only approximately accura

9. Oxalis

Nature of

ber of Flower

mber of Caps

ge Number of Se

st stamens of short-styled. Le

est stamens of mid-styled. Le

form mid-length stamens. Ille

-form shortest stamens. Ille

test stamens of mid-styled. I

gth stamens of short-styled. Ill

ngth stamens of long-styled. L

ngth stamens of short-styled.

own-form longest and shortest stame

st stamens of short-styled. I

rtest stamens of mid-styled.

test stamens of long-styled. L

wn-form longest stamens. Il

n-form mid-length stamens. I

her, of own-form longest and mid-length

gest stamens of mid-styled. I

ength stamens of long-styled. I

on an average 28.58 seeds. Therefore the fertility of the six legitimate to that of the twelve illegitimate unions, as judged by the proportion of flowers which yielded capsules, is as 100 to 15, and judged by the averag

is r

d on an average 5.62 seeds; but we have no means of judging how near an approach this average makes to that from flowers legitimately fertilised. He also fertilised 45 flowers with pollen from the shortest stamens, and these yielded only 17 capsules, or 31 per cent, containing on an average only 2.65 seeds. We thus see that about thrice as many flowers, when fertilised with pollen from the mid-length stamens, produced capsules, and these contained twice as many seeds, as did the flowers fertilised with pollen from the shortest stamens. It thus appears (and we find some evidence of the same fact with O. speciosa), that the same rule holds good with Oxalis as with Lythrum salicaria; namely, that in any two unions, the greater the inequality in length between the pistils and stamens, or, which is the same thing, the greater the distance of the stigma from

of which differ in diameter as 100 and 83), and not one produced a capsule. I formerly cultivated during several years the short-styled form of a species purchased under the name of O. Bowii (but I have some doubts whether it was rightly named), and fertilised many flowers with their own two kinds of pollen, which differ

, a large field of young sugar-cane, many acres in extent, covered with the red blossoms of one form alone, and these did not produce a single seed. His own land is covered with the short-styled form of a white-flowere

of a white colour and quite destitute of pollen; others which are pale yellow contain many bad with some good grains; and others again which are bright yellow have apparently sound pollen; but he has never succeeded in finding any fruit on this species. The stamens in some of the flowers are partially converted into petals. Fritz Muller after reading my description, hereafter to be given, of t

iophytum)

at this plant resembles in this respect O. Valdiviana and Regnelli. Calling the length of the two lobes of the stigma of the long-styled form 100, that of the mid- styled is 141, and that of the short-styled 164. In all other cases, in which the stigma in this genus differs in size in the three forms, the difference is of a reversed nature, the stigma of the long-styled being the

D SPECIES

dely distributed European species, O. stricta and corniculata. Fritz Muller also informs me that a similarly constituted species is found in St. Catharina, and that it is quite fertile with its own pollen when insects are

d I at first thought that O. acetosella was trimorphic. But the case is one merely of great variability. The pollen-grains from the two sets of anthers, as observed by Hildebrand and myself, do not differ in diameter. I fertilised twelve flowers on several plants with pollen from a distinct plant, choosing those with pistils of a different length; and 10 of these (i.e. 83 per cent) produced capsules, which contained on an average 7.9 seeds. Fourteen flowers were fertilised with their own pollen, and 11 of these (i.e. 79 per cent) yielded capsules, containing a larger average of seed, namely 9.2. These plants, therefor

Oxalis are tending towards a dioecious condition, as Zuccarini and Lindley inferred from the diffe

[SP.?] (PON

el with the anthers of the shorter stamens in the long-styled form. The anthers of the longer stamens of the short-styled form are to those of the shorter stamens of the long-styled form as 100 to 88 in length. The pollen-grains distended with water from the longer stamens of the short-styled form are to those from the shorter stamens of the same form as 100 to 87 in diameter, as deduced from ten measurements of each kind. We thus see that the organs in these two forms differ from one another and are arranged in an analogous manner, as in the long and short-styled forms of the trimorphic species of Lythrum and Oxalis. Moreover, the longer stamens of the long-styled form of Pontederia, and the shorter ones of the short-styled form are placed in a proper position for fertil

lour of their corollas, that of the short-styled being of a darker blue, whilst that of the long-styled tends towards violet, and no other such case is known. Lastly, the three longer stamens alternate with the three shorter ones, whereas in Lythrum and Oxalis the long and short stamens belong to distinct whorls. With respect to the absence of the mid-styled form in the

f the short-styled as 100 to 16. Its summit is rectangularly bent upwards, and the stigma is rather broader than that of the mid-styled, and broader in about the ratio of 7 to 4 than that of the short-styled. In the mid-styled form, the stigma is placed rather above the middle of the corolla, and nearly on a level with the mid-length stamens in the other two forms; its summit is a little bent upwards. In the short-styled form the pistil is, as we have seen, very short, and differs from that in the other two forms in being straight. It s

en-grains, after having been long soaked

ource of Po

2: di

ngth stamens (Average of

hortest stamens (10

ngest stamens (15 m

ortest stamens (20

longest stamens (20

id-length stamens (2

rms differ considerably in diameter; as do those in a lesser degree from the corresponding mid-length stamens in the two forms; whilst those from the corresponding shortest stamens in the long- and mid-styled forms are almost exactly equal. Their inequality in the two first cases depends on the grains in both sets of anthers in the short-styled form being smaller than those from the corresponding anthers in the other two forms; and here we have a case parallel with that of the mid-styled form of Lythrum salicaria. In this latter pl

grains of the longer stamens are "more than twice the diameter or than eight times the mass of the grains of the shorter stamens. Though minute, these smaller grains seem as perfect as the larger ones." (4/16. 'Bulletin of the Torrey Botanical Club' 1875 volume 6 page