Elements of Structural and Systematic Botany

ALG? (Ph

; ii, from the side. B, Fragillaria (?). C, Navicula. D, F,

the most part large seaweeds. The diatoms, which are placed in this class simply on account of the color, are probably not closely related to the other brown alg?, but just where they should be placed is difficult to say. In some respects they approach quite closely the desmids, and are not infrequently regarded as related to them. Th

ttached by a gelat

en from above, but there is great variety in this respect. The cell wall is always impregnated with large amounts of flint, so that after the cell dies its shape is perfectly preserved, the flin

other like a pill box and its cover. This arrangement is

ances; but like the movements of Oscillaria and the desmids, the movements are

hat the desmids in

ue Bro

ength in some cases of a hundred metres or more, and showing

, section through a conceptacle containing o?gonia (og.), × 25. C, E, successive stages in the development of the o

t of disc or root from which springs a stem of tough, leathery texture, and forking regularly at intervals, so that the ultimate branches are very numerous, and the plant may reach a length of a metre or more. The branches are flattened and leaf-like, the centre traversed by a thickened midrib. The end of the growing branches is occupied by a transversely elongated pit or depression. The growing point

e most part, and buoy up the plant, bringing

e elevations from which may often be seen protruding clusters of hairs like those arising from the other parts of the plant. A section through one of these enlarged ends shows that each elevation corresponds to a cavity situated below it. O

e shipped for long distances. If they are to be studied away from the seashore, sections for microscopic examination should be mounted in salt water (ab

ilaginous substance derived from the altered outer walls of these cells. This mucilage is hard when dry, but swells up enormously in water, especially fresh water. The cells grow smaller and more compact toward the outside of the section, until there are no spaces o

lusters on the margins of the main branches, and probably become detached, forming new plants. In so

the enlarged ends of some of the branches. In the species here figured, F. vesiculosus, the antheridia and o?

rwoven filaments, from which grow inward numerous hairs, filling up th

r terminal one, the o?gonium proper. The latter enlarges rapidly, and its contents divide into eight parts. The division is at first indicated by a division of the central portion, which includes the nu

. 27, H). Finally, the walls separating the inner cells of the o?gonium become also absorbed, as well as the surrounding membrane, a

the contents of the antheridium are forced out into the water (G), leaving the empty outer wall behind, but still surrounded by a thin membrane. After a few minutes this membrane is dissolved,

hin a few minutes after putting the o?gonia into water, the egg cells may be seen to escape into the water, when some of the antheridia may be added. The spermatozoids will be quickly discharged, and collect immediately in great numbers about the egg cells, to which they apply themselves closely, often setting them in rotation by the movements of their cilia, and presenting a most extraordinary spectacle (J). Owing to the small size of the sperm

into the water. J, a single egg cell surrounded by spermatozoids. K, mass of spermatozoids surrounded by the inner

nched filaments, but most are large plants with complex tissues. Of the latter, a familiar example is the common kelp, "devil's apron" (Laminaria), often three to four metres in length, with a stout stalk, provided with root-like organs, by which it

sporangium, × 150. C, kelp (Laminaria), × ?. D, E, gulf weed (Sargassum). D, one-h

s found from Cape Cod southward (Fig. 28, D, E). These plants possess distinct stems and leaves, and there are