28 SURVEY OF THE REPRODUCTIVE PROCESS 



and some Palmelleae.* In Palmella itself Mr Thwaites 

 figures a branched filament proceeding from a spinulose 

 cell very like a conjugate spore and bearing ordinary 

 palmella-cells at its free extremities. ( And so in Diato- 

 macese, from the frustules developed in conjugation being 

 much larger than their parents, it is probable that they also 

 split up into smaller pieces or frustules. J 



The conjugate spore, whatever be its mode of develop- 

 ment, is always very retentive of vitality, and is commonly 

 several months of germinating. Hence it is fitted to perpe- 

 tuate the race from year to year, and is frequently spoken 

 of as the resting or winter-spore. Bodies of a similar kind 

 are found even in tribes in which as yet no conjugation 

 has been observed, but in these cases we have no satisfac- 

 tory information concerning their mode of origin. The dis- 

 semination of the species under circumstances which admit of 

 continuous vegetation, is effected by zoospores or motile 

 gemmae, very similar of those of the higher Algse. 



Remarkable as the process of conjugation undoubtedly is, 

 and quite different from all other modifications of the re- 

 productive process in the vegetable kingdom, it is very 

 doubtful if the species in which it occurs can be definitively 

 marked off from others, as constituting a natural group of 

 themselves, for in many, which certainly seem to be closely 

 allied to those now under consideration, fertilization ap- 

 pears to be effected, as in the higher algae, by phytozoa. 

 Corpuscules of this nature are described by Carter in the 

 remarkable unicellular alga Vohosc, which ranked so long as 

 an infusory animalcule. In other cases again, as in Cylin- 

 drospermum, among Nostochinese, the filaments are termi- 



* Quar. Journ. Micros. Science, IV., 313. 



f Ami. Nat. Hist., 2d Ser., II. 313. 



J Thwaites' Ann. Nat. Hist., XX. (1847). Griffith Ann. 3d Ser. XVI- 

 92, 1855. 



Annals of Nat. Hist., 3d Ser., II., 237, III. 1. 



