ALGAE. — CONFERVOIDEAE. 45 



the cell appears to be enclosed in a long sheath, the lower portion of the old cell-wall, and 

 this portion in a cell so elongating is always separated from the upper portion which 

 bears the caps by a transverse septum. In Bulbochaete the growth of all the shoots, even 

 of the first that proceed from the germinating spores, and consequently the cell-multipli- 

 cation also, is confined to the division of the basal cells, so that the cells of every shoot 

 must be regarded as the basal cells of their lateral shoots. Each cell contains 

 chlorophyll-corpuscles and a nucleus in a parietal layer of protoplasm. The swarm- 

 spores, oogonia, and antheridia are formed from the cells of the filaments, which swell 

 out into a more or less spherical shape only when oogonia are formed in them. The 

 oospores remain at rest for a considerable time and give birth to swarm-spores (usually 

 four in number) which produce asexual plants, that is plants producing only swarm- 

 spores, from which similar plants proceed repeatedly, till at length the series is closed 

 by the appearance of a sexual generation which forms oospores ; but the sexual plants, 

 the female especially, produce swarm-spores as well. The sexual plants are either 

 monoecious or dioecious, in many species the female plant produces peculiar bodies, 

 termed androspores, which give rise to very small male plants (dwarf males) ; in Oe. 

 diplandrimi the androspores proceed from male plants. Several cycles of generation 

 or only one may be completed in a period of vegetation. A sivariii-spore is formed in 

 an ordinary cell of a filament, sometimes even in the first cell (Fig. 21, E), by contraction 

 of the whole of the cell-protoplasm ; the cell then parts across into two very unequal 

 portions (as in the division of the cells), and the swarm-spore is set free (Fig. 21, /?,/>", is), 

 enveloped at first in a hyaline vesicle. Its hyaline end— the anterior end in the moving 

 state — is furnished with a circlet of many cilia. This end lay laterally in the mother- 

 cell, and when movement ceases it becomes the lower fixed end and dcvelopes into a 

 rhizoid. The direction of growth therefore of the young plant is perpendicular to that 

 of the mother-cell. The spermaiosotds are similar in form to the swarm spores, but 

 much smaller (Fig. 22, i?, 0), and move about like them by means of a circlet of cilia. 

 The mother-cells of the spermatozoids are cells of a filament, but shorter and less rich in 

 chlorophyll than the vegetative cells ; they lie isolated or as many as twelve together 

 one above the other in the filament. In most species every such mother-cell (anther- 

 idial cell) divides into two similar special mother-cells, each of which produces a sper- 

 matozoid ; the spermatozoids escape by the rupture of the mother-cell as in the case of 

 the swarm-spores (Fig. 22, D). The androspores from which the dwarf males proceed 

 are formed in mother-cells like those of the spermatozoids, but there is no formation of 

 special mother-cells ; they settle after swarming on a definite spot of the female plant, 

 on the oogonium or near it, and there germinate and produce at once the antheridial 

 cells and spermatozoids in them (Fig. 22, A, B, tn, m). The oogoniiiin is always developed 

 from the upper daughter-cell of a vegetative cell which has just divided, and which 

 enlarges immediately after division into a spherical or ovoid form. In Bulbochaete 

 the oogonium is always the lowest cell of a fertile branch ; this is not opposed to the 

 law of growth stated above, since the mother-cell of a branch is at the same time its 

 basal cell ; the oogonium of Bulbodiaete is never the first cell of a branch, for this 

 always developes into a bristle. The oogonium first becomes filled more full of cell- 

 contents than the other cells ; then just before fertilisation the protoplasm contracts 

 and forms the oosphere, as in Vaucheria, the chlorophyll-granules being crowded together 

 in its interior ; the part of the oosphere which is turned towards the place where the 

 oogonium opens contains only hyaline protoplasm, and this is where impregnation 

 takes place. The opening of the oogonium is affected in a variety of ways, in many 

 species of Oedogoniiim and in all oi Bulbochaete an oval hole is formed in the side of the 

 cell-wall, through which the colourless portion of the oosphere protrudes in the form of 

 a papilla in order to receive the spermatozoid. In other species (Fig. 21, A^ B) the 

 oogonium breaks across, as the cells do for the release of swarm-spores, and then the 

 filament with its usually straight row of cells appears as if broken at the spot. From 

 the lateral aperture there issues a colourless mucilage which forms itself under the eye 



