GENERAL CHARACTERS OF D I ATOM A C E^l. 277 



172. Diatomacece. Notwithstanding the very close affinity, 

 which, as will be presently shown, exists between this group and 

 the preceding, many Naturalists who do not hesitate in regarding 

 the Desmidiacese as Plants, persist in referring the Diatomacese 

 to the Animal kingdom. For this separation, no valid reason 

 can be assigned ; the curious movements which the Diatomaceee 

 exhibit, being certainly not of a nature to indicate the possession 

 of any truly animal endowment ; and all their other characters 

 being unmistakably vegetable. Like the Desmidiacese, they are 

 simple cells, having a firm external coating, within which is in- 

 cluded a mass of endrochrome whose superficial layer seems to 

 be consolidated into a sort of primordial utricle. The external 

 coat, however, though it seems to have a basis of organic mem- 

 brane, 1 is consolidated by silex; the presence of which in this 

 situation is one of the most distinctive characters of the group. 

 The endochrome, instead of being bright green, is of a yellowish- 

 brown ; and its peculiar color seems to be in some degree de- 

 pendent upon the presence of iron, which is assimilated by the 

 plants of this group, and which may be detected even in their 

 colorless silicified envelopes. The coloring substance appears to 

 be a modification of ordinary chlorophyll; it takes a green or 

 greenish-blue tint with sulphuric acid ; and often assumes this 

 hue in drying. The endochrome consists, as in other Plants, of 

 a viscid protoplasm, in which float the granules of coloring 

 matter. In the ordinary condition of the cell, these granules are 

 diffused through it with tolerable uniformity, except in the cen- 

 tral spot which is occupied by a nucleus; round this nucleus 

 they commonly form a ring, from which radiating lines of 

 granules may be seen to diverge into the cell-cavity. At certain 

 times, oil-globules are observable in the protoplasm ; these seem 

 to represent the starch-granules of the Desmidiacese ( 163) and 

 the oil-globules of other Protophytes ( 151). A distinct move- 

 ment of the granular particles of the endochrome, closely re- 

 sembling the circulation of the cell-contents of the Desmidiaceae 

 ( 164), has been noticed by Prof. W. Smith in some of the larger 

 species of Diatomacese, such as Surirella biseriata, Nitzschia scalaris, 

 and Campylodiscus spiralis; and although this movement has 

 not the regularity so remarkable in the preceding group, yet its 

 existence is important, as confirming the conclusion that each 

 Diatom is a single cell (the endochrome moving freely from one 

 part of its interior to another), and that it does not contain in its 



1 A membrane bearing all the markings of the siliceous envelope has been found by 

 Prof. Bailey to remain, after the removal of the silex by hydrofluoric acid ; and this 

 membrane seems to have been presumed by him, as also by Prof, W. Smith, to lie 

 beneath the siliceous envelope, and to secrete this on its surface as a sort of epidermis. 

 The Author agrees, however, with the authors of the " Micrographic Dictionary" (p. 

 200), in considering it much more likely that this membrane is the proper " cellulose 

 coat" interpenetrated by silex; especially since it has been found by Schmidt, that after 

 removing the protoplasm of Frustulia salina by potash, and the oil by ether, a substance 

 remained identical in composition with the cellulose of Lichens. 



