246 THALLOPHYTES. 



and apex of growth can be distinguished, and a kind of branching makes its 

 appearance. 



Although zoogonidia, in the sense in which the term is used in the higher 

 Thallophytes, do not occur (with the exception of some Palmellaceae which perhaps 

 do not belong to this class), many Protophytes are nevertheless endowed with a 

 power of motion by means of which they swim about ; spirally-wound multicellular 

 filaments turn on their axis; or the filaments themselves bend backwards and 

 forwards; or some other kind of motion occurs. 



No sexual organs have yet been observed, and in most cases there are no 

 non-sexual organs of reproduction, the multiplication of individuals being effected 

 by the separation of the ordinary vegetative cells \ In other words, organs for 

 nutrition and reproduction are not differentiated; it is only in the most highly 

 developed forms that cells of peculiar form are produced for the sole purpose of 

 reproduction. 



The class has hitherto been divided into three groups distinguished by their 

 colour; viz. i. those containing pure chlorophyll, Palmellaceae ; 2. those in which 

 the chlorophyll is mixed with a blue pigment, and which therefore appear of a li^ht 

 green or bluish green colour, Cyanophyceae ; and 3. those in which there is no 

 chlorophyll, Schizomycetes and Yeast. While limiting the class of Protophyta 

 to these three groups, it is nevertheless possible that some of the forms included 

 in it are not independent species, but merely stages in the development of other 

 higher Thallophytes, which have a perpetual power of reproducing themselves. 

 Thus it has already been determined^ that the genus PleurococcuSy hitherto placed 

 among Palmellacese, is merely a stage of development of Chlamydomonas which 

 belongs to Pandorineae, a class of Zygosporese; and it is not improbable that 

 the whole group of Palmellaceae, and perhaps also some Chroococcaceae, are 

 of the same nature, and must at some time be eliminated from the class of 

 Protophyta. 



FORMS CONTAINING CHLOROPHYLL. 



A. CYANOPHYCEiE. These organisms are of a bluish, emerald, or brownish green, 

 or some similar colour, due to a mixture of true chlorophyll and phycocyanin ; this 

 pigment becomes diffused out of dead or ruptured cells, and thus produces the blue 

 stain on the paper on which Oscillatorieae are dried. From crushed specimens 

 treated with cold water phycocyanin is extracted as a beautiful blue solution, 

 blood-red in reflected light ^. When the crushed plants are treated with strong alcohol 

 after the extraction of the blue pigment, a green solution is obtained which contains 

 true chlorophyll, and probably a special yellow pigment, phycoxanthin*. 



I. The Chroococcace89 exist as isolated roundish cells or in roundish families, the 

 cells of which are imbedded either in an amorphous mucilage or in the swollen walls 

 of their mother-cells. They occur as gelatinous growths in damp places. Several 

 genera are distinguished, with numerous species : — e.g. Chroococcus and GlcEocapsa 



* [Gonidia have been discovered in Glceocapsa by Bornet (Ann. sci. nat., sen V. XVII; in 

 Nostoc by Janczewski (ib. XIX), and in Bacillus by Cohn (Beit, zur Biol. d. Pflzn. I).] 



^ Cienkowski, Bot. Zeit. 1865, no. 3 ; and Rostafinski, Bot. Zeit. 1871, p. 786. 



3 Cohn, in Schulze's Archiv fiir mikrosk. Anatomic, vol. III. p. 12. — Askenasy, Bot. Zeit. 1S67. 



* Millaidet and Kraus, Comptes Rendus, vol. LXVI. p. 505. 



