THE ALG^E 



105 



are multinucleate, the ordinary cells may be transformed, without change of 

 form, into oogonia or antheridia, the former containing several egg-cells, the 

 latter very numerous spermatozoids. 



The oogoiiiuin in CEdogoniuni is usually the upper of the two cells formed 

 from division of one of the older cells, so that several of the characteristic caps 

 can usually be seen at the top of the oogonium (Fig. 75, A). Immediately after 

 the division, the cellulose ring stretches out quickly, swelling out at the same 

 time, so that the oogonium is broader than the vegetative cells. Sometimes the 

 lower of the two cells also becomes an oogonium. The cell-contents at first fill 

 the oogonium, but later they contract, becoming denser, also, much as in the for- 

 mation of a swarm-spore. Generally at the apex, or slightly at one side, there 

 is visible ar clear space, much like that at the ciliated end of the swarm-spore. 



B 



FIG. 75. A, oogonium of CEdogonium stagnate (X450). B, antheridium of the 

 same species. C, autheridium of (E. Boscii (X600). D, spermatozoid of same 

 species. E, F, fertilization in (E. Boscii ; sp, the spermatozoid within the egg-cell ; 

 in F, the wall has begun to form about the spore. (?, female plant of (E. 

 macrandrum, with several dwarf males, <5, attached to it (X 450). (C-F, after 

 KLEBAHN.) 



This is the " receptive spot," and it is here that the spermatozoid penetrates the 

 egg-cell. At maturity the oogonium opens, either by a pore near the top or by 

 the filament bending somewhat and leaving the top of the cell open, just as 

 when a swarm-spore is to escape. However, in the oogonium, a new cell-wall 

 is formed within the open space, and in this a pore is developed for the 

 entrance of the spermatozoid. 



Antheridium. The antheridium (Fig. 75, B, C) consists of a series of short 

 cells, formed by the rapid division of a vegetative cell, with very little elongation 

 of the daughter-cells. The antheridium may be upon the same plants which 

 bear the oogonia, or they may be upon different ones. In the latter case, they 

 are often very small male plants ("dwarf males"), which, growing from 

 special swarm-spores (Androspores), attach themselves to the female plants. 



