210 THEIR VEGETABLE NATURE ESTABLISHED. 



place in the household of Nature. Like their mistress, 

 these, her humblest servants, work in secret. We know 

 not what we owe them. But continued, as their exist- 

 ence is, through all time, and dispersed, as they are, 

 through every part of the world even where the ice- 

 bound sea is peopled by nothing else we may rest 

 assured that they do perform some work which renders 

 them worthy the care of a Providence who creates 

 nothing superfluous. I have spoken of the Diatomacece 

 as vegetables. Ehrenberg and many other writers re- 

 gard them as infusorial animals ; and indeed they have 

 been bandied about from the animal to the vegetable 

 kingdom at various times, according to the views of 

 different naturalists. Latterly the evidence seems to 

 have preponderated on the vegetable side, especially 

 since the brilliant discoveries of Mr. Thwaites,* com- 

 municated to a late meeting of the British Association, 

 have shown that their fructification is precisely analo- 

 gous to that of some of the lower Algee, and that the 

 fruit resembles a spore. 



A similar mode of fruiting is now discovered among 

 Desmidiece, which were also classed with Infusoria by 

 Ehrenberg, and of these a large number, in fruit, are 

 figured in the work of Mr. Ralfs, before alluded to ; but 

 as they are natives of fresh water, it is out of place to 

 enter on their history here. I may, however, remark, that 

 the curious spiny bodies found fossilized in flint, which 

 often pass for Xanthidia, are now proved to be only the 

 spores of various genera of jDesmidie<x, whose full-grown 

 fronds are amazingly unlike the spore in form. The 

 * See Thw. in " An. Nat. Hist." N.S. vol. i. p. 162, &c. 



