21 



if an opening be made in one of the segments the contents of 

 both will escape thereout ; and, moreover, we observe granules 

 passing the whole length of the frond without impediment. 

 A further proof lies in the conjugation of the cells and the 

 formation of sporangia. The formation of one sporangium 

 only at the point of contact of the two fronds does not accord 

 with the notion of each frond having two cells. 



The multiplication of cells bj transverse division is full of 

 interest, if only on account of its being the principal mode of 

 reproduction in the protozoa. The process is exhibited as 

 observed by me in a species of Closterium at page 4, fig. 2, of 

 the accompanying book of illustrations. The fission takes 

 place at the centre on the line of division of the two 

 segments, the constriction becoming deeper and deeper until 

 separation ensues. During the process the endochrome in 

 each segment gradually separates and assumes the position of 

 that in the mature plant, vide fig. 2, 6. On separation, the 

 obtuse end becomes pointed, fig. 2, c, and lengthens out until 

 complete development is attained. 



It has been recorded that probably the Desmidiacese are 

 truly reproduced only in two modes ; the one by the escape of 

 the granular contents immediately after the swarming process, 

 and the other by the formation of sporangia, resulting from 

 the conjugation of the cells. Late authorities mention four : 

 first, cell division ; second, the retraction of contents from 

 parent cells and transformation of same into ciliated zoospores ; 

 third, division of cell contents into a number of zoospores ; 

 fourth, conjugation. My own observations on the Closterium 

 striatolatum lead me to add another mode, viz., by the forma- 

 tion of a spore in each segment of the frond without conju- 

 gation, vide illustrations, page , figs 1, lb. Ic. Whilst in 

 coupling one sporanguim results from the connection of two 

 fronds, we have here two spores in each frond. I made a 

 large gathering of the C. Striatolatum this summer, and failed 

 to find any of them in a state of conjugation, although it is 

 commonly observed in this Desmid ; whilst in all those suffi- 

 ciently mature, I found spores as depicted in the figures, 

 besides great numbers of them in the water free from the 

 fronds. Fig. Ic. shows the frond ruptured and the spore 

 ready to pass out. The ultimate history of these spores I 

 shall endeavor to trace through the ensuing winter and spring. 

 The universality of the Desmidiese can be readily understood 

 when we find their germs protected in indurated spore cases 

 such as these. They may be wafted by the wind, or carried 

 by various animals to any distance, when meeting with suitable 

 conditions they burst into life. Darwin mentions fine dust 

 clouds, which, on examination, were found to contain a large 



