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Practical Plant Biology. 



other bifurcations of the branch are also attached to the common 

 base. 



When the sperms emerge from the superficial cells of the 

 antheridium they are carried by currents in the surrounding water, 

 and apparently their numbers are sufficient for chance alone to 

 secure that at least one will reach almost every trichogyne. Once 

 a sperm touches a trichogyne it adheres to it and the thin mem- 

 brane of the trichogyne dissolves at the point of contact, and the 

 protoplasm of the sperm forms connection with that of the carpo- 

 gonium. The nucleus now moves out of the sperm and passes 



FIG. 21. Polysiphonia. On the left, ends of branches and cystocarps, 

 x no. On the right, a, procarp, longitudinal section, x 600. a, carpo- 

 gonium ; b, trichogyne ; c, auxiliary cell ; d, young cystocarp. (Partly 

 after Oltmanns.) 



down along the trichogyne and fusing with the nucleus of the 

 carpogonium forms the oosperm. 



The cytoplasm of the carpogonium is stimulated by this fusion 

 to develop a papilla, which grows toward the adjacent auxiliary 

 cell. The nucleus of the oosperm divides and one segment of it 

 moves into the papilla. The latter continues its growth through 

 the cell-wall and finally penetrates into the auxiliary cell and 

 unites the cytoplasm of the carpogonium with that of the aux- 

 iliary cell. Along this connecting bridge the segment of the 

 oosperm nucleus passes and takes up its position in the auxiliary 

 cell. The process reminds one strongly of the formation of the 



