THALLOPHYTES 



59 



Female plant. — In Polysiphonia the procarp includes several cells 

 in addition to the carpogonium and trichogyne. The carpogonium 

 arises from a large cell of the axis, called the pericentral cell, and around 



FlGS. 149-15 1. — Polysiphonia : 149, showing the polysiphonous bodies bearing two 

 clusters of antheridia; 150, cystocarp, showing the sterile jacket investing the group of 

 carpospores, and also an isolated carpospore; 151, two mother cells forming tetraspores. 



this cell a group of auxiliary cells is formed, one of which crowds between 

 the pericentral cell and the carpogonium. This whole complex struc- 

 ture — trichogyne, carpogonium, pericentral cell, and auxiliary cells 

 — is the procarp (fig. 153). 



Fertilization occurs as in Nemalion, the floating sperm (antheridium) 

 coming in contact with the trichogyne and discharging into it its contents. 

 The male nucleus passes to the carpogonium and there fuses with the 

 female nucleus. The fusion nucleus divides within the carpogonium, 

 and then what are called cell fusions begin. A passageway is opened 

 from the carpogonium, through the intervening auxiliary cell, and into 

 the pericentral cell, and by this means the two daughter nuclei of the 

 fusion nucleus are free to migrate into the pericentral cell. At the same 

 time, the auxiliary cells begin to fuse with one another and with the 

 pericentral cell, until a large, irregular, multinucleate cell or chamber is 

 formed. In this irregular chamber the two nuclei from the carpogonium 

 begin a series of successive divisions, which result in a large number <>f 



