328 



THALLOPHYTES 



the carpogonium and trichogyne. The pericentral cell, the large 

 cell of the axis from which the carpogonium arises and the vege- 

 tative cells, known as auxiliary cells, surrounding the carpogo- 

 nium take part in forming the cystocarp and are therefore con- 

 sidered a part of the procarp. So in polysiphonia a procarp 



FIG. 283. Polysiphonia violacea. A, a part of a plant showing the branch- 

 ing and multicellular character of the filament ( X 75) ; B, a branch bearing 

 antheridia, some of which have broken away (X 400); C, branch bearing 

 a procarp consisting of carpogonium and adjacent cells at c and trichogyne 

 (0 to the tip of which a sperm is attached ( X 500) ; D, branch bearing a 

 mature cystocarp (cy) from which carpospores are shown escaping through 

 an opening in the jacket of the cystocarp (X 75); at the right is a part 

 of a tetrasporic plant bearing three tetrasporangia ( X 100) . 



consists of trichogyne, carpogonium, pericentral cell, and auxiliary 

 cells. 



After fertilization, which is essentially the same as in Nemalion, 

 the carpogonium, pericentral cell, and auxiliary cells unite in 

 forming a large chamber from which lobes arise, and on the ends 

 of these lobes the carpospores are produced. In the meantime 

 vegetative cells, growing up from below, form a jacket which en- 

 closes the spore-bearing structure, thus completing the formation 

 of the cystocarp (meaning a fruit case), which in this plant is a 

 genuine cystocarp. From this cystocarp the carpospores escape 

 and upon germination produce an asexual or tetrasporic plant. 



