IN THE VEGETABLE KINGDOM. 29 



nated by a pair of cells, of which the proximal forms a spore 

 in its interior, while the distal, which goes under the name 

 of heterocyst, has been considered to contain spermatic 

 matter, though no motile particles have been seen to issue 

 from it, nor anything of the nature of fusion or conjugation 

 been observed to take place between it and the spore-cell. 

 Clear cells, to which the name of heterocysts has also been 

 applied, occur in most other Nostochinese, but without the 

 accompanying sporangia, so far as has yet been observed.* 

 There are besides other species in which neither conjugation, 

 nor indeed any form of digenesis, has yet been detected. 

 This is the case, for instance, with the Oscillatorieae, and 

 Ulvaceae, which are not known to multiply but by the de- 

 tachment of cells or frustules, and in the case of the latter 

 also by the emission of zoospores. It is asserted, however, 

 by Itzigsohn that Oscillatoria is only a particular phase of 

 Chlamydococcus, a unicellular alga allied to Palmella the 

 filaments of the former arising from minute spiral corpus- 

 cules, generated within green gonidia discharged from the 

 latter ; while the frustules of the Oscillatoria are stated to 

 be again developed into the globules of chlamydococcus.^ 

 The subject at least invites farther investigation, for there 

 is a prevailing impression among botanists that the Oscilla- 

 toriese are merely barren phases of plants which may fruc- 

 tify in some other form. Among the Ulvaceae it is to be 

 noticed that in some species motile corpuscules occur of two 

 kinds, borne on different plants, one quadriciliate, the other 

 biciliate. The former are regarded by Robin as phytozoa, 

 but Thuret alleges that both kinds germinate. If phytozoa 

 exist we should expect to meet also with corresponding 

 bodies of the nature of resting-spores, but such have not 

 yet been detected, at least in the majority of the group. 



* M. G. Thuret Ann. Nat. Hist., 3d Ser., II. 1. 

 t Quarterly Journal of Micros. Science, II., 188 (Botanische Zeitung). 



