IX THE VEGETABLE KINGDOM. 25 



the following account of the process : " The conjugation 

 ordinarily takes place between the cells of distinct filaments ; 

 these approximate to each other, and put forth little pro- 

 tuberances that coalesce, and establish a free passage 

 between the cavities of the cells, whose contents then inter- 

 mingle."* In reality, however, the outer walls of the con- 

 jugating cells are probably as passive in this as in the 

 former cases, the papilla being protruded, and eventually 

 ruptured at the point of contact by the force of growth of 

 the contained endochrome or portions of the wall already 

 beginning to soften. The united contents on their fusion 

 appear to undergo condensation, and the common mass is 

 generally retracted wholly into one of the original cells."!" 



In the germs Zygnema, and in most other species of the 

 group, the conjugation takes place solely or chiefly between 

 the cells of two filaments which lie parallel to each other, 

 so as to present with their connecting passages a ladder-like 

 appearance ; but in some it takes place promiscuously on 

 all sides, interweaving the whole mass of filaments into an 

 inextricable network. There are also species in which the 

 conjugation takes place between the adjacent cells of the 

 same filament : in this case a channel of communication is 

 formed through a protuberance just over the septum, the 

 contents of one ceh 1 thus escaping into the other, and then 

 forming the spore ; so that after the process is completed 

 the alternate cells contain spores, the intermediate ones 

 being empty. In all these cases the recipient cell, as the 

 matrix of the spore, may, with a certain propriety, be con- 

 sidered to have a female character ; and when, as in the 

 germs Spirogyra, all the cells of one filament thus empty 

 themselves into those of andther, the sexual distinction 



* Principles of Compar. Physiol., p. 190. 



t This is the case also in a species of Didymoprium, one of the filamen- 

 tous Desmidieae. Half s Monograph, pp. 58 62. 



C 



