116 INTEODUCTION TO CRYPTOGAMIC BOTANY. 



animal and vegetable life, if we wish them to agree with fact, 

 and not with mere arbitrary theories. 



95. If the genus Protococcus is to be confined to simple forms, 

 it is clear that several of the so-called species referred to it by 

 Kiitzing, must be erased ; it is, however, certain that some of 

 the substances in question are mere elements of other pro- 

 ductions, and that, inasmuch as the species must either be 

 propagated by the individualising of the granules contained in 

 their protoplasm, or by the division of the protoplasm by dis- 

 sepiments, we must either have two series of forms, or two 

 modes of propagation must be common to the genus, if not 

 to every individual in it.* The phaenomena exhibited by 

 P. pluvialis are rather in favour of the former view ; and if 

 so, it will be impossible to distinguish some of the larger Pro- 

 tococci from such genera as Glceocapsa, the characters of 

 which depend upon the higher development of the spores, 

 and the numerous coats of which the cellular walls consist. 

 The fact is, however, that the limits of the numerous genera 

 proposed by authors, and more especially by Kiitzing, are by 

 no means fixed. Indeed, Kiitzing himself looks upon many of 

 his species as mere forms, but if every form is to have a name, 

 there will be no limit to spurious species, and no chance of 

 ever arriving at a natural arrangement; for it is clear that, if 

 in nature there is really a distinct plan, every intrusive species 

 must tend to derange it, or to render the plan itself obscure. 

 Kiitzing indeed points out, in his work on German Alg^, 

 different species of Scytonema, of which he believes certain 

 kinds of Glceocapsa to be forms. This and many other similar 

 points were long since detailed to me, by Mr. Thwaites, in the 

 course of an almost daily correspondence ; but unfortunately 

 he was unable to publish the full result of his observations 



* It is probable, that wherever propagation takes place by the mere 

 division of the endochrome without any transformation, we have either 

 early stages of other Algae and Cryptogams, or mere propagation by ger- 

 mination. In some species. Zoospores are produced, in others, spores 

 by copulation, and similar appearances may hereafter be discovered in 

 all. Some Desmidiaoece and DiatomacetB may grow for years without 

 forming a spore, the propagation being carried on meanwhile by mere 

 division. 



