V^n the vast territory of the freshwater algee, which was shrouded in 

 almost total darkness no longer than twenty years ago, as to the know- 

 ledge of their development and systematic arrangement, the excellent 

 researches of Pkingsheim, Cohn and De Baey have thrown an imespected 

 light. The profoimd morphological inquiries of these men have enriched 

 science with the knowledge of a not inconsiderable number of orders of 

 algse, more nicely distinguished from each other and of much greater 

 importance and interest, on account of the history of their development, 

 than most other orders of plants. Nevertheless a great number of algas 

 stiU remains almost unknown as to the history of their development and 

 their place in the system. Among these are to be counted the Clado- 

 phoreœ^ existing as well in salt and brackish, as in fresh water, and extre- 

 mely rich in varying forms. We have, however, believed we knew, 

 that their propagation was effected, as a rule, by naked, moving, ciliated 

 spores, — so-called zoospores. This is indisputably the case with many, 

 or perhaps wdth most of the plants that have been coimted among the 

 Cladopliorece. But that this is not the case with all the forms that have 

 been referred to this genus, is proved by the researches of which I 

 am now going to give an account. 



My attention was directed to Cladophorece during a sojourn at the 

 magnificent botanical institution at Kew in England, in the summer of 

 1872, by an alga which occurred in great abundance in its Tropical 

 Aquarium, or the so-called Waterlily-house. It resembled in its general 

 habitus a common Cladophora^ but was distinguished by most of the 

 specimens having, besides the common long and slender cylindric cells, 

 others somewhat swollen, short, and very rich in chlorophyll, which 

 were almost always single, and most frequently alternated in a regular 



Nova Acta Reg. Soc. Sc. Ups. Ser. III. 1 



