18 DESMIDS OF THE IXITKI) STATES. 



There are some peculiarities attending the process of multiplication. 

 The new semi-cells are nor always exact counterparts of the mother 

 semi-cell. Plate XV, fig. 18, Cosmrtrium m on il [forme ; here there 

 is an enlargement of the new, central semi-cells, probably developed 

 under more favorable circumstances than the original cell. An 

 impoverished condition is more frequently the result. Plate XXX 

 is a striking illustration of such an instance in Micrasterias 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 typecontinue 

 indefinitely, the original form would soon be lost, 1 mt the true type 

 as described nearly forty years ago by Prof. Bailey is preserved to 

 this day. The changes are probably due to an impoverished con- 

 dition 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, figs. 712 show how the separated, 

 floating joints of a Hyalotheca 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 a- represented in the 

 figures of the progressive stages (figs. 1<>, 11) to the perfected 

 zygospore (fig. 1*2). The three circular forms united, are the 

 divided cells or semi-cells. 



Plate [II, fig. 3, are two cells separated from the filament (fig - . 1) 

 drawn together ami united by a gelatinous tube mutually protruded : 

 through this the green cellular contents (Chlorophyl) of the one, 

 passes out into the other, thus producing the regenerated spore, (fig. 4). 



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

 separated in each joint. How together, (fig. !J) and condense; 

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

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

 reproduction ; two cell- are drawn together, when they unite (tig. 6) 

 and hind themselves closely until they fuse into one body, (figs. 8, 9). 



Plate VIII, fig. 2, is another instance, varying only in form, the 

 two cells in the first stage of conjugation ; tig. ">, the developed 



