158 
F. E. Frit sell. 
doubtless many, so to say, cosmopolitan epiphytes which will grow 
on any sort of substratum, but a considerable number of them are 
probably more particular and are influenced by conditions like those 
just indicated. Nor are epiphytes the only forms exhibiting these 
features; the tangle of every filamentous Alga affords shelter to a 
larger or smaller community of Protococcales, Desmids, Diatoms, 
etc., and there is evidence that here also we have no casual pheno¬ 
menon, but that many of these forms are confined to the tangles of 
one or other species of Alga. In some cases (especially in the 
attached algal growth on submerged rock-surfaces) we find a number 
of filamentous Algae densely intertwined with one another to form 
compact masses, often including a certain number of unicellular 
forms. Such dense algal felts undoubtedly show much the same 
composition in pieces of water far apart from one another; their 
object seems to be in the first place a protective one against the 
ravages of aquatic animals, but it is quite possible that more 
important (nutritive ?) inter-relations exist, which we are at present 
not in a position to determine. The preceding remarks will suffice 
to show the necessity of noticing the inter relations amongst the 
different members of the algal vegetation of a piece of water. I 
have elsewhere proposed the term consortium (^fellowship, parti¬ 
cipation) for such intimate connections of algal forms; there is a 
closer relation in these cases than between the different members 
of an association and so a separate designation seems warranted ; a 
consortium carries us half-way towards symbiosis. 
I will now return once more to the periodicity of aquatic vege¬ 
tation. The great difference between the ecological study of 
terrestrial and aquatic plants lies in the very marked seasonal 
variations of the latter. In the case of a terrestrial flora the plants, 
which constitute a formation, are represented in it throughout the 
greater part of the year; some of them will be more prominent in 
some months than in others owing to flowering or numerical 
preponderance, but all persist throughout the greater part of the 
period of vegetation and are always to be found amongst the members 
of the given formation. In an aquatic flora on the other hand 
matters are very different; in most cases a number of dominant 
forms succeed one another in the course of a year 1 and after their 
1 Cf. the table on p. 164 ; also Fritsch, Algol. Notes. IV. Remarks 
on the periodical development of the Alga: in the artificial 
waters at Kew. Annals of Bot., Vol. XVII., No. LXV., 1903, 
pp. 274—278; and Alga:, in The wild Fauna and Flora of the 
Royal Botanic Gardens, Kew. Bull. Miscell. Inform., Roy. 
Bot. Gards., Kew. Addit. Scr. V., 1906, p. 190. 
