INTRODUCTION. 25 



similar to those of the Conjugate, and are no less permanent 

 in their nature. 



M. Decaisne combats the idea of the disintegration of the 

 spores of the Alga formed by the union of the endochrome 

 of two cells into zoospores. He states the fact, that the 

 contents of the spores are fluid. This argument is, however, 

 by no means conclusive ; the contents of the undoubted 

 zoosporous Algce are, also, for the most part, fluid; Avhen, 

 however, the full developcment has been attained, the fluid 

 disappears, and the cells are filled with zoospores. The same 

 may occur in the spores of the Zygnemata &c., as asserted to 

 be the case by Agardh. 



]\I. Decaisne also, in his " Memoir on the Classification of 

 the Alga,'' strongly repudiates the idea of a double mode of 

 reproduction. The spores, IM. Decaisne regards, as already 

 remarked, as the true and only reproductive bodies of those 

 AlgcR in which they occur, and asserts that in these Algce 

 zoospores are never formed. M. Decaisne thus clearly ex- 

 presses himself on this point : " Mais je crois pouvoir avancer 

 aujourd'hui que les zoosporces n'ofFrent jamais de corps re- 

 producteurs resultant d'une concentration de la matiere verte 

 provenant de deux individus." 



This generalization of ]\I. Decaisne is surely untenable, for 

 it is f)crfectiy certain that the usual and most frequent mode 

 of reproduction of the Vesiadiferce, in which spores alto- 

 gether analogous, as before stated, with those of the Conjugates 

 are formed, is by means of zoospores. The motion and de- 

 velopcment of the zoospores of this genus of Alga I have re- 

 peatedly Avitnessed, in such a manner as to preclude all doubt 

 on the question. Now this fact in reference to the Vesiculiferoe, 

 wliicli may be relied on, leads to the adoption of one of the 

 following views, either that there is a double mode of repro- 

 duction in at least a certain number of those Alga in which 

 true spores are formed, viz. by zoospores and spores, or else 

 that the oval bodies termed spores do become disintegrated, 

 in accordance with the statement of Agardh, into numerous 

 zoospores. On the " spores " themselves M. Decaisne has the 

 following remarks : " After the complete organization of the 



