2 COCCOPHYCE.E. 



ORDER I. COCCOPHYCEJE. 



Unicellular alg^e. Cells either single, or many associated in 

 families, tegument involute or naked, destitute of branches or 

 terminal vegetation. Propagation by cell-division or zoogo- 

 nidia. 



This order includes the two families Palmellacece and Protococcacece, 

 with unmoveable cells, to which is attached a third, the Volvocinece, with 

 mobile cells. The two former correspond to the Chroococcacece amongst 

 the class PhycocJiromacece. Although thus removed, it would seem from 

 recent researches, that there is, in some sort, a relationship between the 

 Palmellacece and Protococcacea, on the one hand, and the Chroococcacece 

 on the other. 



We can only direct attention here to the papers by P. Richter, in 

 "Hedwigia,' (xix., 1880, p. 154-) on Glceocystis and (xix. 1880, p. 169 

 and 191), on the " genetic Connection of certain Unicellular PhycocJi- 

 romacece" of which abstracts were published in the " Koyal Microsco- 

 pical Journal."* 



The conclusions arrived at are in favour of a sort of polymorphism. 



" The lowest form of the Phycochromaceaa is the naked Aphanocapsa 

 condition, corresponding to Palmella among the Chlorophyllophyceae. 

 From this naked or only slightly encysted condition is developed the 

 Glceocapsa or Glceocystis form with several gelatinous envelopes ; the 

 Chroococcus type, when the investment is altogether wanting, or, when 

 there is only a single vesicular envelope, the caenobium types. The 

 Glceocapsa type is specially adapted for exposure to the air, and growth 

 upon a comparatively dry substratum ; the caenobium type is developed 

 in water ; the Chroococceus type in water, or on a moist substratum in 

 the air. With this is connected the cylindrical form, a higher stage, 

 because it displays a differentiation in the direction of growth, and a 

 development towards the filiform condition. This is not always de- 

 veloped, and may be distinguished into stable and unstable forms ; the 

 latter may occur in two or three varieties, and may go through the 

 following successive conditions : 



1. Stable Aphanocapsa and Palmella. 



2. Aphanocapsa and Palmella which have attained to Glceocapsa, 

 Glceocystis, or Ceenobium type, but which always revert to the naked 

 solitary spherical form. 



3. Stable Glceocapsa, Glceocystis, Chroococcus, and caenobium forms, 

 without reversion (Merismopedia). 



4. Cylindrical forms, the generations of which pass through the 

 solitary spherical fAphanocapga and Palmella} condition, as well as the 

 Glceocapsa and similar forms. 



5. Cylindrical forms, which pass through only the Glceoeapsa and 

 similar forms. 



6. Cylindrical forms the generations of which revert to the Apliano- 

 capsa and Palmella condition, while the Glceocapsa or any similar form 

 is suppressed. 



7. Stable cylindrical forms CSynecliococcus). 



No reference is made in the above to the passage of Glceocapsa into 

 the encysted filiform conditions of Sirosiphon corresponding to Palmo- 

 dactylon and Hormospora among the Chlorophyllophycese." 



* Vol. I., Second Series, 188, pp. 98 and 201. 



