IP 



78 



PLANT MORPHOLOGY 



sterile cells (paraphyses) , arise in large pat ches on both sides of the thallus 

 (Fig. 64). They produce 32 or 64 small, laterally biciliate zoospores. 

 The reduction of chromosomes results from the division of the nucleus of 

 the young sporangium. After four or five simultaneous free-nuclear 

 divisions have taken place, the contents of the sporangium undergoes 

 cleavage into uninucleate protoplasts, the zoospores. These are liberated 



Fig. 66. Apical portion of a plant of Macrocystis pyrifera, one-fifth natural size. 



and develop into minute male and female gametophytes (Fig. 65). The 

 sperms are laterally biciliate and are borne singly in antheridia that arise 

 at the ends of short, branched filaments. The female plant usually con- 

 sists of only a few cells, one of which becomes an oogonium. This pro- 

 duces a single nonmotile egg that is extruded through a terminal pore, to 

 which it remains attached. The zygote germinates at once, giving rise 

 to the large sporophyte. 



