202 



vant géminés, se multipliant par une division spontanee (déduplica- 

 tion) transversale, commc cela arrivo dans quelques autres Pleuro- 

 coccoidées. Une division analogue a lieu dans les Desmidiées, aux- 

 quelles on serait d'abord tenté de rapporter les Hormospora ; mais 

 les demi-corpuscules (hémisomates) des Desmidiées développent à 

 leur point de séparation une nouvelle portion semblable à la pre- 

 mière, tandis que, dans l' accroissement des Nostocinées, les corpu- 

 scules sont divisés en deux par un etranglement transversai, sans 

 qui'! s'ensuive une reproduction sur chacun des points de rupture. 

 11 y a dans ce cas, comme je l'ai dit ailleurs, dédiiplicatioii simple. 

 Dans les Desmidiées, il y a dcduplication et r è duplica ti 07t ». 



It is with unseigned difjìdence that 1 venture to dissent from 

 the opinion of one possessing so profound a knowledge of these 

 tribes, and I do so only from conviction, the result of dose and 

 repeated investigations. 



I bave stated my beleif that the same changes occur in both the 

 Desmidieae and the Nostochineae. A celi in Micrasterias has two he- 

 mispheres, just as a joint in Anabaina has; in both these separate, and 

 in both each hemisphere becomes again a perfect sphere; and if 

 in Micrasterias the two hemispheres are united by their whole bases, 

 these would not remain even an apparent difference between them. 



The production of Desmidieae in newly-formed collections of 

 water is involved in obscurty. The late M. Miller of Penzance pointed 

 out to me an instance of this kind well-worthy of notice. He found 

 Hyalotheca dissiliens and other species of this family in an old water- 

 batt which stord is a yard remote from any apparent station for the 

 Desmidieae, and derived its water from the clouds alone; and the 

 question naturally arisses. How came the Algae there? The theory 

 of spontaneous generation has never obtained curiancy in this king- 

 dom, and for my own post I am not unwilling to alknowledge 

 that these are mysteries in nature which we cannot penetrate. I 

 can therefore only attempt to account for the appearance of the 

 Dismidieae under such circumstances in two ways, - by supposing 

 either that the atmosphere contains countless myriads of the Desmi- 

 dieae and other Cryptogamae, which vegetate only when they meet 

 a congenia situlation, or that the seeds we conveyed by means of 

 aquatic insects, many of which, it is well known, svam during the 



