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F. E. Frit sell. 
the more important results to be attained by a study of algal 
periodicity; there are numerous other minor problems, which will 
also find solution in this line of research, some of which will be 
pointed out below. For some years past 1 have been collecting 
periodic data of this kind with the kind help of a number of 
provincial Botanists; the arduous task of working through the large 
mass of accumulated material has been to a great extent undertaken 
by Miss F. Rich, who has also contributed materially by her own 
collecting. The detailed results so far obtained we hope to publish 
towards the end of the year. 
There is still a third point of view from which we can study 
aquatic vegetation ; it is by far the most difficult, and we cannot 
expect to obtain many results until our knowledge of the above 
points is more advanced. I refer to the study of the inter-relations 
between the different members of the vegetation of a piece of water. 
Statistics obtained from periodical and casual observation will help 
us to determine these inter-relations precisely, but the conditions 
involving their existence will only be settled by experiment. 
An important question, which presents itself at the outset of 
the study of Algal Ecology, is the determination of the unit; what 
are we to call a formation ? A terrestrial plant-formation consists 
of a collection of more or less numerous species, which are all 
adapted to the same kind of environment, frequently have a similar 
habit and form a coherent whole. The entire submerged flora of 
our waters constitutes a biological group, whose chief peculiarity 
lies in the method of nutrition and gaseous interchange owing to 
the special conditions of the environment; submerged aquatics are 
comparable with epiphytes, parasites, carnivores, etc., all of which 
are biological groups owing their special character to some 
common peculiarity. The members of these different biological 
groups are, however, characteristic of diverse formations, since 
other features of their structure (apart from the common biological 
peculiarity) adapt them to different kinds of environments; this is 
most noticeably the case amongst parasites. We are then con¬ 
fronted in the first place by the question: Are submerged aquatics 
also to be split up and relegated to different terrestrial formations, 
or in other words, are the species populating a given piece of water 
dependent on the nature of the surrounding terrestrial vegetation ? 
It is not impossible that there are relations of this kind, but it does 
not seem likely that they will be fundamental. Probably it will be 
found that the submerged flora of woodland pools for instance is 
