INTRODUCTION. 33 



little it proceeds towards the centre, and in place of a zone of 

 liquid substance there is a membrane duly organized and 

 fit to become divided into two membranes, each mass of 

 endochrome having its wall, or more correctly, its proper 

 membrane." In this account no mention is made as to 

 whether the cells, the division of which M. Morren witnessed, 

 were terminal or not. 



My own views of the phenomenon of the division of the 

 cells of Conferva, and of the explanation to be offered of it, 

 differ considerably from those of M. Morren. All the cells 

 of a Conferva, until it has reached a state of maturity, are 

 continually increasing in length ; and it is only in certain cells 

 which have exceeded their standard length, that the gradual 

 separation of the endochrome into two masses is seen to 

 occur, and a transparent space to be left between them ; this 

 space is not, however, in my opinion, occupied by any form- 

 ative intercellular matter, such as that referred to by M. 

 Morren, who, in his explanation, asserts that the polarization 

 and separation of the endochrome first takes place, and that 

 afterwards the cells begin to grow. The first indication of 

 the formation of the partitions which are to divide the parent 

 cell into two, is not visible until after the separation of the 

 endochrome, and appears to consist in a solution of a portion 

 of the periphery of the centre of that cell, the divided edges 

 of the cell then becoming inverted separately, and growing 

 towards the centre, where they coalesce. Thus, according to 

 this view, the partitions of the cells are not, as M. Morren 

 would assert, new growths or formations, but merely an 

 extension of the separated margins of the parent cell. 



A second mode of development *, of considerable import- 

 ance as regards the classification and description of the Alga, 

 still remains to be described. In many species of Conferva 

 more especially in the branched kinds, and in numerous other 

 Algce ; in the species of the genera Vesiculifera, Lyngbya, 

 Meloseira, Fragilaria, &c., there is not only a longitudinal de- 

 velopement of the cells, but there is likewise a lateral growth 



* See Annals of Nat. Hist. vol. xi. p. 359. 

 D 



