ZVGNEMACE.E. 75 



We append here De Bary's scheme of classification of this Order, 

 which he terms " Conjugate." 



" Cells of limited growth, propagated by unlimited repeated biparti- 

 tion (tripartite in Craterospermum) in the same direction, free or con- 

 nected in single rows, chlorophyll in parietal bands, axile plates, or 

 radiating bodies, in pairs. Cell-wall cellulose or gelatinous. 



"Fructification. By copulation a zygospore arises of a different form 

 from its mother-cells. No asexually produced swarmspores. 



" SUBDIVISIONS. 



"I. Mesocarpeee. Zygospore the shape of the mother-cells, not con- 

 tracted, separating by three or five partitions into a central firm-walled 

 resting-spore and two or four lateral decaying cells. (Cells cylindrical, 

 united in threads, with axile plates of chlorophyll.) 



"II. ZygnemefS. Zygospore undivided and mostly contracted, passing 

 into the resting condition, afterwards developing into a germ-cell divided 

 into a basal cell, and a thread-cell capable of division. (Cells cylin- 

 drical, united in threads.) 



" III. Desmidiece. Zygospore of the form of the Zygnemece, develop- 

 ing into a germ-cell, or divided into 2 or 4, each of which separates into 

 two equal daughter-cells capable of division. (Cells usually consisting 

 of two symmetrical halves, of very various form, free or united.)" 



We have adopted a similar arrangement, with the exception of the 

 present exclusion of the Desmidiece, and the addition of a small sub- 

 family, the Gronatonemece, which dates from a period subsequent to 

 De Bai'y's Memoir. 



Conjugation in the present family is the union of two cells, either of 

 separate filaments, or of the same filament, the result being the forma- 

 tion of a zygospore. The cells containing the male and female element 

 cannot at present be distinguished from each other, although De Bary 

 states that he has observed a constant difference between the fertile and 

 sterile cells of a species of Spirogyra. Usually all the cells of one 

 filament appear to be either giving or receiving cells, so that the male 

 and female filaments would seem to be distinct, but this requires more 

 certain confirmation, inasmuch as in such of the species of Sjjirogyra as 

 exhibit lateral as well as scalariform conjugation, all the cells in one 

 filament cannot be of the same kind. 



" The first perceptible change in a cell about to produce a resting. 

 spore appears to be a loosening of the primordial utricle from the outer 

 wall, and a contraction of it upon the cell-contents, which thus are 

 crowded together and more or less deformed. Simultaneously with 

 this, or a little after or before it, the side wall of the cell is ruptured, and 

 a little pullalation or process is pushed out, which directly coats itself 

 with cellulose and rapidly enlarges to a considerable diameter, at the 

 same time growing in length until it meets a similar process pushing out 

 from an opposing cell, or has attained as great a length as its laws of 

 development will allow. When two processes meet they become fused 

 together, the end walls are ruptured, and the contents of one cell pass- 

 ing over are received within those of the other, or else the contents of 

 both cells meet within the connecting tube, arid there fuse together. 

 This is the more common mode of conjugation, in which two cells of 

 distinct filaments become joined together by a connecting tube. It is 

 evident that, if the filaments are fertile to their fullest extent, there 

 will be as many of these connecting tubes as there are pairs of cells 

 in the filaments, and a ladder-like body will be formed, the ori- 

 ginal filaments corresponding to the side pieces, the connecting tubes 

 to the rounds. Hence this method of conjugation has received the 

 name of scalariform. 



" In the so-called lateral conjugation, instead of cells of different 

 filaments joining, adjacent cells of one filament unite together to com- 



M 



