CHAPTER III. FECUNDATION ; NON-MOTILE 

 ISOGAMETES. 



In this chapter will be discussed the sexual process in several forms 

 in which the gametes are non-motile, z. ., they do not escape from 

 the parent plant and move about in the surrounding media, and are 

 either unisexual or show a certain degree of bisexuality, as in Basidio- 

 bolus. The forms used, Spirogyra, Cosmarium and Closterium 

 among the desmids, certain diatoms and Basidiobolus, have been 

 chosen solely because the development of the gametes and their union 

 have been most thoroughly investigated in certain species of these 

 genera. Owing to the conflicting results obtained by the several 

 investigators in the much-studied Sporodinia, the process in this plant, 

 which properly belongs here, will be only incidentally referred to. 



FIG. 19. Copulation of gametes in Ectocar^us siliculosus. 



A, female gamete with numerous male gametes attached, seen from the side. 



B, C, D, E, successive stages of cytoplasmic fusion. (After Berthold.) 

 E, F, G, fusion of nucleus. (After Oltmanns.) 



SPIROGYRA. 



Among the algae Spirogyra undoubtedly furnishes the best known 

 illustration of the sexual process in which the gametes are isogamous 

 and non-motile. The process as observed in the living plant has been 

 carefully described long ago by DeBary ('58), Strasburger ('78) and 

 others, and it is now a matter of common observation in almost every 

 botanical laboratory. The nuclear behavior, which cannot be fol- 

 lowed in the living specimen, and which is the most essential part of 

 the process, has received comparatively little attention. 



Morphologically and physiologically every cell of a Spirogyra 

 filament, except those serving as organs of attachment, is exactly like 

 every other cell, so that the filament may be regarded, in a sense at 



