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 



Figs. 149— 151. — 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 auxihary 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 nu cleus divides within the carpogoniu m, 

 and then what are called cell tusions beg m. A passageway is op pnpri 

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

 the pericentral cell, and by this means the two daughte r nurlf^i nf thp 

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

 time, the aux iliary cells begin to fuse with one another and with the 

 perice ntral cell, until a large, irregular, multinucleate cell or chamMTyjs 

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

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



