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. e., 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 Basédzo- 
éolus. The forms used, Spzrogyra, Cosmarium and Clostertum 
among the desmids, certain diatoms and Bastdzobolus, 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 inthe much-studied Sforodinza, the process in this plant, 
which properly belongs here, will be only incidentally referred to. 
os 
Fic. 19.—Copulation of gametes in Ectocarpus 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 alge Sfrogyra 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 (778) 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 
