The Classification of the Algce. 119 



In several genera of this class of Algae, swarm-cells have not 

 been observed. The conjugation of these plants must take 

 place, therefore, by means of still or vegetative cells. Among 

 the Confervae or thread-like plants, as well as among the Des- 

 mids, and with certain modifications, also among the Diatoms, 

 conjugation happens, in general, in the following manner : two 

 threads, or more exactly two fronds, place themselves side by 

 side, the cell-walls of each touching those of the other ex- 

 ternally. Soon, at the point of contact, the cell-wall is ab- 

 sorbed, and a passage between the two vegetative cells is pro- 

 duced. Through this passage the contents of one of the cells 

 pass over into and mingle with that of the other. This new 

 mass seems to acquire a power not possessed by either of its 

 constituent elements, and immediately proceeds to clothe itself 

 with a thick cell-wall, and rounds out into an oblong or egg- 

 shaped, dense mass of green protoplasm, forming thereby the 

 Zygospore. 



This, immediately, or after resting a longer or shorter time 

 according to the habits of the genus, grows into a new plant, 

 or else segregates itself into smaller spores sometimes into 

 swarm-spores, which in their turn produce the new plant. 



The illustrations of this process, drawn from life from the 

 Confervae, especially the genus Spirogyra, and from the Desmids, 

 are so common in works of botany and books on the micro- 

 scope, that it is not deemed necessary to reproduce them here. 



The characteristic fact of this reproductive process is the 

 conjugation of two cells of like and undistinguishable nature, 

 whether they be swarm-cells or vegetative cells. 



OOSPORE-ffi. 



The next higher step in the reproductive process of the 

 Algae is characterized by the conjugation of two cells of unlike 

 size and distinquishable qualities, and also by the fact that the 

 larger — oftentimes a thousand fold larger e^g cell — is always 

 fixed upon some part of the plant, and is fructified by the 

 pressing upon and into it, of the spermatozoids, or very 

 minute swarm-cells, which go swimming by. 



On the plants of the genus Vaiecheria, numbers of short 

 one or two celled branches grow out near each other. Some of 

 these always remain slender, and have in their contents but lit- 

 tle chlorophyll, being filled mostly with colorless protoplasm. 

 These branches are the antheridia, and produce from their cell- 



