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. 



