DESMIDE^E. 339 



tracts forcibly on the application of certain reagents, the 

 action of which cannot be considered as purely chemical; 

 and second, that iodine does not detect the presence of starch 

 in the cells. The former observation is equally applicable 

 to the tender membrane which lines the cells of true Con- 

 ferva, while the latter remark is wanting in accuracy, for 

 it is only when the Desmidece are very young, and before 

 the contents of the cells assume a granular appearance, that 

 iodine does not make manifest the presence of starch ; subse- 

 quently, however, when the endochrome has become granular 

 and vesicular, starch is readily detected by means of iodine, 

 it turning the large vesicular granules of a blue colour. 



Meyen advocated the vegetability of the Desmidea, and 

 was the first to detect the presence of starch in the cells, but 

 the accuracy of his remarks has been doubted ; they are now, 

 however, fully confirmed by Ralfs, Jenner, and the majority 

 of recent algologists. 



The DesmidecB, I conceive then, are to be regarded as 

 vegetable productions, agreeing with the Conferva proper, of 

 whose vegetability there can be no question, in the following 

 particulars. 



1st. Probably in the elementary composition of the cel- 

 lular tissue. 



2d. In the undoubted presence of starch in the cells. 



3d. In the multiplication of cells by division. 



4th. In their reproduction. 



The reproduction of this family has been stated by some 

 writers to be threefold. I am disposed to think, however, 

 that there is but one essential and true mode of reproduc- 

 tion. The three methods by which the Desmidece are stated 

 to be multiplied are, first, by the division of the cells ; 

 second, by bodies analogous to zoospores ; and third, by 

 true spores, formed as in the Conjugates, by the union, 

 intermingling, and condensation of the contents of two 

 distinct individuals. To the family Conjugates indeed the 

 DesmidecB would appear to be more nearly related than to 

 any other. The first cannot be regarded as a true mode of 

 reproduction ; it is but a continual growth, repetition, and 



z 2 



