The Different Forms of Flowers on Plants of the Same Species

eris or t

structure betwe

ity when legitimately a

garis, Sinensis

ity of the heterostyl

species o

ia pal

ce vita

.1. Primu

ong-sty

hort-sty

has hitherto been looked at as a case of mere variability, but this view, as we shall presently see, is far from the true one. Florists who cultivate the Polyanthus and Auricula have long been aware of the two kinds of flowers, and they call the plants which display the globular stigma at the mouth of the corolla, "pin-headed" or "pin-eyed," and those which display the anthers, "

short-styled it is depressed on the summit, so that the longitudinal axis of the former is sometimes nearly double that of the latter. Although somewhat variable in shape, one difference is persistent, namely, in roughness: in some specimens carefully compared, the papillae which render the stigma rough were in the long- styled form from twice to thrice as long as in the short-styled. The anthers do not differ in size in the two forms, which I mention because this is the case with some heterostyled plants. The most remarkable difference is in the pollen- grains. I measured with the micrometer many specimens, both dry and wet, taken from plants growing in different situations, and always found a palpable difference. The grains distended with water from the short-styled flowers were about .038 millimetres (10 to 11/7000 of an inch) in diameter, whilst those from the long-styled were about .0254 millimetres (7/7000 of an in

n the unexpanded and unimpregnated flowers of the latter are considerably larger than those of the short-styled flowers (1/3. 'Natural History Review' July 1862 page

high above the anthers. The stamens are short; the grains of pollen smaller and oblong in shape. The upper half of the tube o

stigma standing beneath the anthers. The stamens are long; the grains of pollen are spherical and larger. The t

er, as did some in my garden which flowered out of their proper season in the autumn. Mr. W. Wooler, of Darlington, however, informs us that he has seen early blossoms on the Polyanthus, which were not long-styled, but became so later in the season. (1/4. I have proved by numerous experiments, hereafter to be given, that the Polyanthus is a variety of Primula veris.) Possibly in this case the pistils may not have been fully developed during the early spring. An excellent proof of the permanence of the t

urred to me was, that this species was tending towards a dioecious condition; that the long-styled plants, with their longer pistils, rougher stigmas, and smaller pollen-grains, were more feminine in nature, and would produce more seed;-that the short-styled plants, with their shorter pistils, longer stamens and larger pollen-grains, were more

LE

n 1:

Number o

mber of Umbe

mber of Caps

eight of Se

owslips : 9 :

wslips : 13 :

d from an equal number of umbels, and from an equal number

LE

n 1:

Number o

eight of Se

.

Number o

: Weight

.

Number o

eight of Se

ps : 10 : 92 :: 100

ps : 10 : 70 :: 10

he number of umbels (which is the fairest standard, for large and small plants are thus equalised), th

f wild plants had been transplanted during the previous autumn into

LE

n 1:

Number o

Number o

eight of Se

cowslips : 47

cowslips : 5

ve us the follow

LE

n 1:

Number o

eight of Se

.

Number o

eight of Se

slips : 100 : 15

slips : 100 : 1

the actual produce of seed was considerably larger. Nevertheless we have the same relative result; for the short-styled plants produced more seed than the long-styled in nearly the proportion

ive than the long-styled form, and the same result holds good with some other species of Primula. Consequently my anticipation that the plants with lon

gh other umbels on the same plants, artificially fertilised, produced an abundance of seed; and this fact shows that the mere covering in itself w

LE

n 1:

Number o

mber of Umbe

: Produc

1.3 grain weight of seed

: 18 : 74 :

some other minute insect. It is scarcely necessary to give any additional evidence, but I may add that ten pots of Polyanthuses and cowslips of both forms, protected from insects in my greenhouse, did not set one pod, though artificially fertilised flowers in other pots produced an abundance. We thus see that the visits of insects are absolutely necessary for the fertilisation of Primula veris. If the corolla of the long-styled form had dropped off, instead of remaining attached in a wither

ed, and this favours their pollen being deposited on it. It follows from the position of the organs that if the proboscis of a dead humble-bee, or a thick bristle or rough needle, be pushed down the corolla, first of one form and then of the other, as an insect would do in visiting the two forms growing mingled together, pollen from the long-stamened form adheres round the base of the object, and is left with certainty on the stigma of the long-styled form; whilst pollen from the short stamens of the long-styled form adheres a little way above the extremity of the object, and some is generally left on the stigma of the other form. In accordance with this observation I found that the two kinds of pollen, which could easily be recognised under the microscope, adhered in this manner to the proboscides of the two species of humble-bees and of the moth, which were caught visiting the flowers; but some small grains were mingled with

s, and "homomorphic" to the illegitimate unions; but after discovering the existence of trimorphic plants, in which many more unions are possible, these two terms ceased to be applicable. The illegitimate unions of both forms might have been tried in three ways; for a flower of either form may be fertilised with pollen from the same flower, or with that from a another flower on the same plant, or with that from a distinct plant of the same form. But to make my experiments perfectly fair, and to avoid any evil result from self-fertilisation or too close interbreeding, I have invariably employed pollen from a distinct plant of the same form for the illegitimate uni

6. Primu

Nature of

ber of Flower

mber of Caps

umber of go

eight of Se

d Weight of Seed fr

ort-styled. Legitimate unio

ollen. Illegitimate union

ong-styled. Legitimate unio

pollen. Illegitimate unio

MM

e unions : 35 : 2

te unions : 35 : 1

or of the good alone, produced by 100 flowers of both forms when legitimately and illegitimately fertilised; secondly,

7. Primu

Nature of

ber of Flower

Number o

umber of go

eight of Se

.

Number o

eight of Se

.

umber of go

eight of Se

ns : 100 : 77 : 71 : 39

ons : 100 : 45 : 31 : 11

onal weight of seeds than do the flowers of the long-styled when fertilised with pollen from a distinct plant of the same form. So it is with the short-styled flowers, if treated in an analogous manner. Therefore I have calle

.2. Primu

ation of two kind

ong-sty

hort-sty

58. Returning to Table 1.7, if we consider only the good capsules, those from the two legitimate unions were to those from the two illegitimate in number as 71 to 31, or as 100 to 44. Again, if we take an equal number of capsules, whether good or bad, from the legitimately and illegitimately fertilised flowers, we find that the former contained seeds by weight compared with the latter as 50 to 24, or as 100 to 48; but if all the poor capsules are rejected, of which many were produced by the illegitimately fertilised flowers, the proportion is 54 to 35, or as 100 to 65. In thi

use to too hot a sun, and a large number of umbels perished. Some, however, remained in moderately good health, and on these there were twelve flowers which had been fertilised legitimately, and eleven which had been fertilised illegitimately. The twelve legitimate unions yie

al bodies of different sexes, so here we have two bodies, approximately equal in number, differing in their sexual powers and related to each other like males and females. There are many hermaphrodite animals which cannot fertilise themselves, but most unite with another hermaphrodite. So it is with numerous plants; for the pollen is often mature and shed, or is mechanically protruded, before the flower's own stigma is ready; and such flowers absolutely require the presence of another hermaphrodite for sexual union. But with the cowslip and various other species of Primula t

849 page 216.) With P. veris, for every 100 seeds yielded by the two legitimate unions, only 64 were yielded by an equal number of good capsules from the two illegitimate unions. With P. Sinensis, as we shall hereafter see, the proportion was nearly the same- -namely, as 100 to 62. Now Gartner has shown that, on the calculation of Verbascum lychnitis yielding with its own pollen 100 seeds, it yielded when fertilised by the pollen of Verbascum Phoeniceum 90 seeds; by the pollen of Verbascum nigrum, 63 seeds; by that of Verbascum blattaria, 62 seeds. So again, Dianthus barbatus fertilised by the pollen of D. superbus yielded 81 seeds, and by the pollen of D. japonicus 66 s

s be saved from complete barrenness. But the advantage is not so great as might at first be thought, for the seedlings from illegitimate unions do not generally consist of both forms, but all belong to the parent form; they are, moreover, in some degree weakly in constitution, as will be shown in a future chapter. If, however, a flower's own pollen should first be placed by insects or fall on the stigma, it by no means follows that cross-fertilisation will be thus prevented. It is well known that if pollen from a distinct species be placed on the stigma of a plant, and some hours afterwards its own pollen be placed on it, the latter will be prepotent and will quite obliterate any effect from the foreign pollen; and there can har

of seeds, which the capsules contained. A smaller proportion, also, of these seeds than of the others germinated, and they germinated more slowly. The sterility of this union is the more remarkable,

ic plants illegitimately fertilised with their own-form pollen, I shall have occasion to sh

elatio

xlip of Eng

esent species resembles to a certain extent in general appearance the common oxlip, which is a hybrid between the cowslip and primrose. Primula elatior is found in England only in two or three of the eastern counties; and I was supplied with living plants by Mr. Doubleday, who,

ity of the two forms, when legitimately and ill

. Primula

Nature of

ber of Flower

er of good Cap

Number of Seeds

Number of Seeds

ge Number of Se

ort-styled. Legitimate unio

: 20 : 4 : 49* : 2 : 27.7. (*These seeds were so po

ong-styled. Legitimate unio

pollen. Illegitimate unio

MM

nions together : 20

49* : 2 : 35.5. (*These seeds were so poor and

egitimately fertilised. If we judge of the relative fertility of the two kinds of unions by the average number of seeds per capsule, the ratio is as 100 to 75. But this latter number is probably much too high, as many of the seeds produced by the illegitimately fertilised long-styled flowers were so small that they probably would not have germinated, and ought

instance with heterostyled plants of equal- styled flowers appearing in a state of nature, though far from rare with plants which have been long cultivated. It is still more remarkable that in eighteen cases the same plant produced both long-styled and short-styled, or long-

aris (var. a

se of Engl

, much magnified and drawn under the camera lucida. The upper and smaller grains

ly, on a level with the anthers of the opposite form; for it was found, from an average of 15 measurements, that the distance between the middle of the stigma and the middle of the anthers in the short- styled form is to that in the long-styled as 100 to 93. The anthers do not differ in size in the two forms. The pollen-grains from the short-styled flowers before they were soaked in water were decidedly broader, in proportion to their length, than those from the long-styled; after being soaked they were relatively to those from the long-styled as 100 to 71 in diameter, and more transparent. A large number of flowers from the two forms were compar

. Primula

Nature of

ber of Flower

er of good Cap

Number of Seeds

Number of Seeds

ge Number of Se

ort-styled. Legitimate unio

llen. Illegitimate union :

llen of long-style

75 : 4

timate union : 18 : 7 : 43 : 5 : 18.8 (

MM

nions together : 20

er : 39 : 21 : 66 : 5 : 35.5 (This

ilised by nocturnal Lepidoptera. The long-styled plants when protected from insects yield a considerable number of capsules, and they thus differ remarkably from the same form of the cowslip, which is quite sterile under the same circumstances. Twenty-three spontaneously self-fertilised capsules from this form contained, on an average, 19.2 seeds. The short-styled plants produced fewer spontaneously self-fertilised capsules, and fourteen of them contained only 6.2 seeds per capsule. The self-fertilisation of both forms was probably aided by Thrips, which abounded within the flowers; but these minute insects could not have

la Si

sche Zeitung' January 1, 1864, and he shows that I erred greatly about the size of the pollen-grains in the two forms. I suppose that by mistake I measured twice over pollen-grains from the same form.) The grains, therefore, of the short-styled are to those of the long- styled in length as 100 to 57. Hildebrand also remarked, as I had done in the case of P. veris, that the smaller grains from the long-styled are much more transparent than the larger ones from the short-styled form. We shall hereafter see that this cultivated plant varies much in its dimorphic condition and is often equal-styled. Some individuals may be said to be sub-heterostyled; thus in two white-flowered plants the pistil projected above the stamen

0. Primul

Nature of

ber of Flower

er of good Cap

ge Weight of Se

.

of Seeds per Capsule as a

asi

hort-styled. Legitimate un

pollen. Illegitimate uni

llen of long-style

: 0.76

wn-form pollen. I

: 0.23

MM

unions together : 3

unions together : 2

roduced by the two kinds of unions, the ratio is as 100 to 63. On another occasion a large number of flowers of both forms were fertilised in the same manner, but no account of their number was kept. The seeds, however, were carefully counted, a

mula Sinensis (

Nature of

ber of Flower

er of good Cap

ge Number of Se

f short-styled. Legitim

n, from a distinct plant. Ill

om same flower. Illegiti

of long-styled. Legitim

n, from a distinct plant. Ille

m the same flower. Illegit

MM

te unions togeth

ions together (own-form

together (pollen from the

hown in a condensed form in Table 1.11. Besides using for the illegitimate unions pollen from a distinct plant of the

oth forms contained fewer seeds relatively to the legitimately fertilised capsules than in my experiments; for the ratio in his case is as 42 to 100, instead of, as in mine, as 53 to 100. Fertility is a very variable element with most plants, being determined by the conditions to which they are subjected, of which fact I have observed striking instances with the present

ct plant of the same form. In the latter case all the flowers produced capsules, whilst only 67 out of 100 of those fertilised with their own pollen produced capsules. The s

lants yielded only half-a-grain weight of seeds. Therefore the long-styled plants yielded nearly 24 times as many spontaneously self-fertilised seeds as did the same number of short-styled plants. The chief cause of this great difference appears to be, that when the corolla of a long-styled plant falls off, the anthers, from being situated near the bottom of the tube are necessarily dragged over the stigma and leave pollen on it, as I saw when I hastened the fall of nearly withered flowers; whereas in the short-styled flowers, the stamens are seated at the mouth of the corolla, and in falling off do

ropagated for about 300 years, and produces, when legitimately fertilised, a large number of seeds; the long-styled forms yielding an average number of 73, and the short-styled 98 seeds per cap

short, rising but little above the ovarium. The pollen-grains of these short stamens, when distended with water, were barely 5/6000 of an inch in diameter, whereas those from the long stamens of the short-styled plants were barely 7/6000, showing a relative difference of about 71 to 100. The smaller grains of the long-styled plant are also much more transparent, and before distention with water more triangular in outline than those of the other form. Mr. Scott compared ten plants of both forms growing under similar conditions, and found that, although the long-styled plant produced more umbels and more capsules than the short-styled, yet t

ith respect to this and the five following species, the paper lately referred to may be consulted. In each case the fertility of the two legitimate unions, taken together, is compared with that of the two illegitimate unions toge

unions of the auricula is to that of the two illegitimate u

a Sikk

in relative length as the pistils. The pollen-grains differ in a marked manner in the two forms; "those of the long-styled plants are sharply triquetrous, smaller, and more transparent than those of the short-

a cort

. The pollen-grains of the short-styled form are, as usual, "larger, less transparent, and more bluntly triangular than those from the long-styled plants." Th

a invo

whilst that of the short-styled is smooth and depressed on the apex. The pollen- grains of the two forms differ in size and transparency as before, but not in

la fa

e two forms differ but little in shape. The pollen-grains differ in the usual manner in size, but not in form. The fertility of the t

GOING HETEROSTYLED

mate Unions, compared with that of the two Illegitimat

: Name o

ons, Judged of by the Prop

oduced C

ions, Judged of by the Av

of Seeds p

veris :

: 27 : 75 (Pro

s : 60 : 54 (Pe

inensis :

sis (second t

s (after Hildeb

icula (Scot

imensis (Sco

usoides (Sco

lucrata (Sco

inosa (Scot

nine species

m taken from a distinct plant, has now been given. The results are seen in Table 1.12; the fertility being judged by two standards, namely, by that of the proportional number of

ised illegitimately and yielded 15 capsules, we may assume that on an average an equal proportion of the flowers in both lots would fail to produce capsules from various accidental causes; and the ratio of 18/20 to 15/30, or as 100 to 56 (in whole numbers), would show the proportional number of capsules due to the two methods of fertilisation; and the number 56 would appear in t

per cent of the illegitimately fertilised flowers of P. Sikkimensis produced capsules; but these contained only 31 per cent of the number of seeds in the legitimate capsules. On the other hand, with P. elatior only 27 per cent of the illegitimately fertilised flowers yielded capsules; but these contained nearly 75 per cent of the legitimate number of seeds. It appears that the setting of the flowers, that is, the production of capsules whether good or bad, is not so much influenced by legitimate and illegitimate fertilisation as is the number of seeds which the capsules contain. For, as may be seen at the bottom of Table 1.12, 88.4 per cent of the illegitimately fertilised flowers yielded capsu

LE

a veri

or : 44 (Prob

ris : 36 (Per

Sinens

auricu

Sikkimen

cortusoi

involucr

farino

e the stigma, their pollen is more likely to fall on it, or to be carried down to it by insects, than in the case of the long-styled form. It appears probable, therefore, at first sight, that the lessened capacity of the short-styled flowers to be fertilised with their own pollen, is a special adaptation for counteracting their greater liability to receive their own pollen, and thus for checking self-fertilisation. But from facts with respect to other species hereafter to be given, this view can hardly be admitted. In accordance with the above liability, when some of the species of Primula

SPECIES O

verticillata, a variety of Sibirica, elata, mollis, and longiflora, are truly homostyled; and to these may be added, according to Axell, P. stricta. (1/14. Koch was aware that this species was homostyled: see "Treviranus uber Dichogamie nach Sprengel und Darwin" 'Botanische Zeitung' January 2, 1863 page 4.) Mr. Scott experimented on P. Scotica, mollis, and verticillata, and found that their flowers yielded an abundance of seeds when fertilised with their own pollen. This shows that they are not heterostyled in function. P. Scotica is, however, only moderately fertile when insects are excluded, but this depends merely on the coherent pollen not readily falling on the stigma without t

ia pal

at of the short-styled, with the stigma rather smaller, though rougher. H. Muller gives figures of the stigmatic papillae of the two forms, and those of the long-styled are seen to be more than double the length, and much thicker than the papillae of the short-styled form. (1/16. 'Die Befruchtung' etc. page 350.) The anthers in the one form do not stand exactly on a level with the stigma in the other form; for the distance between the organs is greater in the short-styled than in the long-styled flowers in the proportion of 100 to 71. In dried specimens soaked in water the anthers of the short-styled form are larger than those of the long-styled, in the ratio of

he illegitimate (1/17. 'Journal of the Linnean Society Botany' volume 8 1864 page 79.); but since the publication of his paper

onia palustris (

Nature of

mber of Caps

ge Number of Se

of short-styled. Legit

en, from a distinct plant. I

of long-styled. Legit

len, from a distinct plant.

MM

ate unions toge

mate unions toge

18. H. Muller says 'Die Befruchtung' etc. page 352, that the long-styled flowers, when illegitimately fertilised, yield as many seeds as when legitimately fertilised; but by adding up the number of seeds from all the capsules produced by the two methods of fertilisation, as given by him, I arrive at the results shown in Table 1.13.

f the same form; and the results are very striking. For the capsules from the long-styled flowers thus treated contained, on an average, only 15.7 seeds instead of 77.5

nited States, does not appear to be heterostyled, but is remarkable from produ

ed specimens of the long-styled forms. But the evidence seems sufficient to leave hardly a doubt that Androsace is heterostyled. Fritz Muller sent me from South Brazil dried flowers of a Statice which he believed to be heterostyled. In the one form the pistil was considerably longer and the stamens slightly shorter than the corresponding organs in the other form. But as in the shorter-styled form the stigmas reached up to the anthers of the same flower, and as I could not detect in the dried specimens