APPENDIX D. Ixi 



tation, there are produced from the Lyiigbya thread broad 

 wavy fronds, the cells of which are held together by colour- 

 less intercellular substance. Such fronds may also throw 

 off gonidia, and these may go through all the changes above 

 described ; or some of its peripheral cells may take on the 

 linear mode of growth. Dr. Hicks says : — ' The whole of 

 these changes are so palpable, can be observed so constantly, 

 and are, at the same time, so simple in their relations to 

 one another, that one can scarcely imagine how they can 

 have been separated, not only into distinct species, but into 

 different families of Algae. Thus the linear stage is called 

 Lynghya ; the early stage of collateral segmentation, Schizo- 

 goniiim; the adult stage Prasiola ^; while the gonidial growth 

 has been classed under Palmellacece. And this has been 

 done by most algologists. Meyer, indeed, had pointed out 

 a connection between them ; but his opinions were denied 

 by Jesseu, and ignored by most others. It is a striking 

 instance of the insuperable tendency of some to look upon 

 every distinct form as a separate species.' The characters 

 of the cells or segments in Lyngbya are subject to changes 

 of all kinds, not only as regards the particular characters 

 of the green colouring matter contained in them, but also as 

 regards the shape and size of the segments. They may be 

 more or less rounded, so as to resemble those of Nostoc, 

 and their length not only varies much in adjacent filaments, 

 but even occasionally in different portions of the same fila- 

 ment. This depends altogether 'upon the rapidity of the 

 process of Hnear subdivision, compared with the rapidity of 

 individual cell-growth. Sometimes the rate of the former 

 is so much in excess, that the cells are no thicker than the 

 septa, the thread appearing to consist of narrow green and 



^ The two latter genera have always been located in the fiimily 

 Ulvacece. 



