*54 
F. E. Fritsch. 
of the most important substrata for the growth of a number of 
epiphytes (Protococcales and Diatoms), which are wanting or poorly 
developed when the Cladophoraceous element is lacking. 
Admitting a classification of pieces of water into those with 
and those without Cladophoraceae, we may next turn our attention 
to the importance of other groups of Algae, viz., Vancheria and the 
Confervales, the Conjugate, Oedogonium , the Ulotrichales and the 
Cyanophyceae. All of these no doubt play an important part as 
character-plants, but space does not permit of more than a brief 
consideration of some of them. The peculiar assimilatory process 
of Vancheria and the Confervales probably makes these forms more 
susceptible to variations in the environment than most other green 
Algae ; it certainly seems as though they will rank second in impor¬ 
tance to the Cladophoraceae as character-forms of aquatic 
formations. These Algae are very rare in tropical freshwaters 
(especially Vancheria), although the exact reasons for their scarcity 
are not yet apparent. Special note should therefore be made of 
the occurrence or absence of Vancheria and Conferva in a piece of 
water. 
The Conjugatae will undoubtedly also furnish a valuable 
feature in the determination of aquatic formations; on the one 
hand the presence or absence of forms of this group is to be noted, 
but in many cases it will be necessary to apply a more detailed 
scrutiny, since certain Conjugate species or genera (e.g., Sfirogyra, 
Zygnema, filamentous Desmids) are certainly of value as character- 
plants; the same remarks apply to the Diatoms. 
Cyanophyceae are probably also important character-plants; the 
large majority of the members of this group have a preference for 
waters of warm temperature, so that they are not found in deep 
waters, which are not much heated by the sun, and are more 
characteristic of shallow lakes and ponds. The blue-green Algae are 
excessively characteristic of tropical freshwater formations to which 
they give a very distinctive stamp. 
The object of the present communication being only to 
indicate the lines of research adopted and one or two of the general 
results, I will refrain from further discussion of details and will 
only point out that looking at the algal vegetation of different 
pieces of water as a whole, one notices that some contain a 
considerable number of broad filamentous forms, while in others 
the prevailing type is that of a relatively narrow filament. This 
distinction is probably frequently a fundamental one due to the 
