ii8 American Quarterly Microscopical Journal. 



formed with some view to reproductive function, as in the 

 Rivularia. In the second class, the 



ZYGOSPORACE^, 



the reproductive act is clearly made out. The changes which 

 take place in the vegetative cell to transform it into the repro- 

 ductive cell, and all the steps of the subsequent processes have 

 been carefully studied and described in a considerable number 

 of species. The reproductive act is called "conjugation." 

 It produces a true spore, named the Zygospore. " Conjuga- 

 tion " is the uniting and commingling of the contents of two 

 like cells. The Zygospore, which results from this act, pro- 

 duces by germination and growth, directly or indirectly, the 

 new plant; i. e., either with or without an intervening " resting " 

 period. There are two distinct methods in this process of con- 

 jugation which divide the class into two unequal groups; viz., 

 the conjugation of "swarm-cells," and the conjugation of un- 

 moving or vegetative cells. Cohn has shown, some years ago, 

 how the first process proceeds in the genus Volvox. Areschoug 

 has made some recent studies in the history of certain marine 

 Confervae which illustrate this point very well. Areschoug has 

 found that many of that group of related plants like Hormiscia, 

 Cladophora, Enteromorpha, etc., produce, by the segmentation of 

 the vegetative cell, two kinds of swarm-cells, distinguished 

 chiefly by marked differences of size, and sometimes also by 

 the larger swarm-cells having four, and the smaller two, cilia. 

 The one he called a " Megazouspore," and the other a " Micro- 

 zoospore." 



Plate XL, Fig. i, a, represents the Megazouspore, and b the 

 Microzoospore of the Enteromorpha compressa, a plant growing 

 common on our New England coast. These spores are produced 

 by changes in the cell-contents of some of the vegetable 

 cells of the plant — the two kinds beingalways produced in differ- 

 ent cells of the plant. They are filled with green protoplasm,, 

 clear at the apex and granulous at the base, with a distinct 

 dark-red granule on the side. Plate XI., Fig. i, c, d, e,f, shows 

 the different stages in the process of conjugation, with the fully 

 formed Zygospore at /. At i^, we see the same already germi- 

 nated, and beginning its growth as a new plant without a rest- 

 ing period. The objects in these figures are magnified i,ooo 

 diameters, and are from Observationes Phycologicae. — J. E. 

 Areschoug. Particula Secunda, 1874. 



