44 8 PROTOPHYTA 



. 



by the star-shaped chromatophores which enclose moderately large 

 pyrenoi^s. It has possibly been erroneously referred to this family. 



Most of the genera and species of Chroococcaceas grow in moist 

 situations, as on damp rocks, where they frequently form large shining 

 blue-green mucilaginous masses ; others swim freely on the surface of 

 bog-pools ; a few are found in salt water, attached to sea-weeds. The 

 gonids or algal constituents of many lichens have been shown to be pro- 

 tophytal organisms belonging to the Chroococcaceae. As it is highly 

 probable that many forms at present included in the family are stages in 

 the history of development of more highly organised protophytes, or even 

 of algae, their place in a final system of classification is altogether un- 

 certain until their life-history has been more thoroughly investigated. 

 Many are closely analogous to corresponding forms among the Protococ- 

 caceae, as Chroococcus to Chlorococcum, Glceocapsa to Gloeocystis, 



N 





FlG. yn.Microcystis marginata Men. FIG. $]%. Caiosphcerhim Kiitzingianum Nag. 

 (x 400). (After Cooke.) (x 400). (After Cooke.) 



Aphanocapsa to Protococcus, Coelosphaerium to Botryococcus, and 

 Merismopedia to Tetraspora; but they are probably merely parallel 

 serie^ of forms without any direct genetic connection. Richter, however, 

 identifies Glceocapsa and Gloeocystis. 



The same observer suggests also a genetic affinity lietween the 

 various genera usually included under the Chroococcaceae of the follow- 

 ing nature. The lowest form is the naked Aphanocapsa-condition, 

 corresponding to Palmella among the Protococcaceae. From this naked 

 or only slightly encysted condition is developed the Gloeocapsa- or 

 Gloeocystis-form, with several gelatinous envelopes, the Chroococcus- 

 condition, where the investment is altogether wanting, and the coenobe- 

 or Ccelosphaerium-condition, where there is only a slight vesicular 

 envelope. The Gloeocapsa -form is especially adapted for exposure to 

 air and growth upon a comparatively dry substratum ; the coenobe-type 

 is developed in wa^er or on a moist substratum in the air. With this 

 is connected the cylindrical form, a higher stage, because it displays 

 differentiation in the direction of growth, and a development towards 



