18 DESMIDS OF THE UNITED STATES. 



cells, probably developed uuder more favorable circumstances- 

 than the original cell. An impoverished condition is more fre- 

 quently the result. Plate XXXIV is a striking illustration of 

 such an instance in Mu'raxteriax Torreyi. Fig. 1 is nearest the 

 typical form described by Bailey, the other seven are varieties 

 which occurred by division. I found them variously attached 

 one to the other; one half distinct from the other half, and some 

 so different from the typical form that had they not been mingled 

 with many others they could easily have been mistaken for other 

 species. Did these departures from the normal type continue 

 indefinitely, the original form would soon be lost, but the true 

 type as described nearly forty years ago by Prof. Bailey is pre- 

 served to this day. The changes are probably due to an impov- 

 erished condition of the plant. This suggests the cause of the 

 second mode of multiplication, viz. : that by 



REGENERATION. 



This process is figured to some extent on many of the plates 

 of our illustrations. Plate I, tigs. 7-12, show how the separated. 

 floating joints of a Hyalatheca are drawn together, and unite by 

 means of a gelatinous tube (fig. 9) into which the contents of the 

 cells gradually empty ; the tube enlarges as represented in the 

 figures of the progressive stages (figs. 10, 11) to the perfected 

 zygospore (fig. 12). The three circular forms united, are the 

 divided cells or semi-cells. 



, Plate III, fig. 3, are two cells separated from the filament (fig. 

 1) drawn together and united by a gelatinous tube mutually 

 protruded; through this the green cellular contents (OUorophyf) 

 of the one passes out into the other, thus producing the regen- 

 erated spore (fig. 4). 



Plate II, fig. 8, is a simpler process; the contents normally 

 separated in each joint, flow together (fig. 9), and condense ; 

 then enlarge (fig. 10) and finally break loose (tig. 11) to produce 

 the new plant. Plate III, figs. 5-9, illustrate another method 

 of reproduction ; two cells are drawn together, when they unite 

 (fig. 6) and bind themselves closely until they fuse into one 

 body, (figs. 8, 9). 



Plate IX, tig. 2, is another instance, varying only in form, tin- 

 two cells in the first stage of conjugation; fig. 3, the developed 

 zygospore with the empty semi-cells or husks still attached. Figs. 

 4, 9, 10, 11, 16, are zygospores of various species of Closterium. 

 This condition of copulation and developed spores. :i/</ospores, or 

 sporangium* as often termed, is frequent ; the next step or GER- 



