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AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
Braun theorem.^ The discovery of the third variable may furnish the key 
to some of those sets of graphs, the curves of which exhibit so marked a 
tendency toward synchrony in the occurrence of their maxima and minima — 
a correspondence that is evident only upon casual inspection and which 
vanishes upon detailed examination, leaving one with the perplexed feeling 
that some relation exists. Possibly dry weight, enlargement, and respira- 
tion may be three such variables, dry weight being considered as indicated 
above, although the choice of proper units will involve difficulties. This 
must be done, however, with individuals, not statistically, if such a relation 
is sought. 
Thus far may we be carried by the discussion of properties of systems 
as a point of view. Further progress, aside from filling in the gaps in this 
outline, initiates the consideration of particular problems and correspond- 
ingly particular methods. There is always danger in discussing generalities 
and avoiding the concrete, and, lest the whole matter be thought of as 
still in the nebulous state of a day-dream, it may be well to state that a 
beginning has been made^ — a beginning which, although modest in its 
comprehensiveness, seems to increase in possibilities and exactness the 
further it is carried. I do not present the data or the method for two 
reasons. First, it seems that a presentation of the general point of view 
would have to be made anyway and is, indeed, of vastly greater importance 
than a presentation of one of its applidations. Leaving the mind undis- 
tracted by numerical data and their symbolic representation may allow 
some one to apply the general principle to problems upon which he is 
engaging himself, instead of inducing him to regard the matter as a problem 
in a field foreign to his own. The second reason is obvious: lack of time. 
Wellesley College, 
Wellesley, Massachusetts 
* Chwolson, O. D. Loc. cit. 476-480. 
^ Some of the early results were presented before the Physiological Section of the 
Botanical Society of America at its Baltimore meeting in 1918, under the title, "Growth 
equilibria in Pinus Strobus." 
