DESMIDIACECE : GENERAL CHARACTERS. 



259 



200. Desmidiacece. — Among the simplest tribes of Protophytes, 

 there are two which are of such peculiar interest to the 

 Microscopist, as to need a special notice ; these are the Desmi- 

 diacece and the Diatomacece. Both of them were ranked by 

 Ehrenberg and many other Naturalists as Animalcules ; but the 

 fuller knowledge of their Life-history, and the more extended 

 acquaintance with the parallel histories of other simple forms of 

 Vegetation, which have been gained during the last twenty years, 



Fig. 110. 



Various species of Staurastrum : — a, S. vestitum ; b, S. acvXeatum ; 

 c, S. parctdoxum ; d, e, S. brachiatum. 



are now generally accepted as decisive in regard to their 

 Vegetable nature. — The Desmidiacece * are minute plants of air 



however, does not accord with the account given above of the relations 

 of its different forms. According to him, V. globator and V. stellatus are 

 essentially distinct ; the former is not monoecious but dioecious, and 

 Spkcerosira xolcox is its male or spermatic form ; whilst the latter is 

 monoecious. — An extremely -interesting Volvocine form described by Cohn 

 under the name Steph(inosplio>ra plurialis exhibits all the phenomena of 

 reproduction by Macro-gonidia or composite masses of adherent cells, by 

 Micro-gonidia or active zoospores, by 'still' or Stato-spores, and by Oo- 

 spores produced by true sexual action, in a very characteristic manner; 

 and his account of its life-history should be consulted by every one who 

 desires to study that of any of the Protophvta. See "Ann. of Nat. 

 Hist." 2nd Ser., Vol. x. (1852), p. 321, and " Quart. Journ. of Microsc. 

 Sci.," Vol. vi. (1858), p. 131. 

 * Our first accurate knowledge of this group dates from the publication 



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