10 INTRODUCTION. 



of this sudden commotion cannot be ascertained ; but I have 

 met with it more frequently in specimens that have been 

 kept some days than in fresh-gathered ones. When released 

 by the opening of the suture, the granules still move, but 

 more rapidly and to a greater distance. With the sub- 

 sequent history of these granules I am altogether unac- 

 quainted, but I conclude that it is similar to what has been 

 traced in other Algse. 



The second mode of reproduction is by coupling, and the 

 formation of sporangia. A communication is established 

 between two cells, and a seed-like mass is formed in the 

 same manner as in the Conjugatse. This is green and gra- 

 nular at first, but soon becomes of a homogeneous appear- 

 ance and of a brown or even reddish colour. There are 

 however some variations in the process in the two families 

 which require notice. In the Conjugatae, the cells conjugate 

 whilst still forming parts of a filament ; but in the Des- 

 midiese, the filamentous species almost invariably separate 

 into single joints before their conjugation, and in most of 

 the species the valves of the cells become detached after they 

 are emptied of their contents. 



In many genera the sporangia remain smooth and un- 

 altered ; in others they become granulated, tuberculated 

 or spinous ; the spines being either simple or forked at the 

 apex. In fact a sporangium may pass successively through 

 all these stages, and hence may so change its appearance 

 that its different states are liable to be taken for sporangia 

 belonging to different species. In Tiresias also we sometimes 

 meet with sporangia bearing spines, but in that genus they 

 are arranged like the spokes of a wheel , and not scattered as 

 in the Desmidiese. What is the nature of the sporangia, 

 and why so complicated a process is necessary, since the 

 species is also propagated by means of the granules or zoo- 

 spores which escape from the ruptured cell, are questions to 

 which we cannot, in the present state of science, return a 

 satisfactory answer. The sporangia I consider capsules ; 

 and this view seems to be confirmed by the experience of 



