102 FRESH- WATER ALGiE. 



by authors, even up to the time of Hassall, cannot be definitely 

 placed on account of this deficiency. 



Cooke describes over 120 genera of fresh-water Algae, some of 

 which contain many species — the genus JB,dogoniuin possessing 

 over 50 species; other genera containing from 12 to 20 species, 

 and fresh species are frequently being described. 



This description includes only British species ; those common 

 to the Continent of Europe generally being much more numerous. 

 Fresh-water Algae have been found in all parts of the world, those 

 from the tropics being often very luxuriant in their growth ; the 

 fresh-water Algae of America have been fully described and illus- 

 trated by Horatio Wood. 



Bibliography. 



Berkeley's Cryptogamic Botany, Hassall's Fresh-Water Algae, 

 Cooke's British Fresh Water Algae, Journal Royal Microscopical 

 Society (new series), Annales des Sciences Naturelles (3rd, 4th, 

 5th, and 6th series), Braun's Rejuvenescence in Nature (Ray 

 Society), Sach's Botany (2nd English Edition), Grevillea, Vols. 

 1-12, etc., etc. 



EXPLANATION OF PLATES IX., X., XL 



Plate IX. 

 Figs. 1-8 — Development of Sorastrum. 



1. — Colony of unicellular individuals. 



2. — A separate cell 



3.-6. — Formation of new cells. 



7. — A new colony. 



8. — A double colony of old and new cells. 



,, 9-11. — Conjugation and production of zygospore in Pandorina. 



,, 12. — The same in Rhizopus. 



,, 13. — Adult form of Pandorina. 



,, 14-15 — Various stages in development into separate plants, con- 

 taining clusters of zoospores. 



Plate X. 

 Fig. 1. — Continuation of Figs. 14-15, PI. 9. 



