Aspects of Ecology. 237 
This frankness cannot be allowed to disarm the critic because 
except in this paragraph the hypotheses are presented with very 
little qualification and because out of multiple hypotheses a clever 
botanist can hardly help creating a beautiful growth which looks 
like a plant but which experiment may prove to be a mirage. 
Though Dr. Clements’ simple hypothetical scheme of correlation 
between factor, function and structure will not stand analysis in its 
present form, yet a more adequate and complex form of it might 
perhaps be constructed by recognizing that some factors affecting 
functions are direct equations of energy while others are stimuli, 
by allowing for the abrupt discontinuance of a relation by limiting 
factors, and by recognising that adaptation is often antagonistic to 
adjustment and almost to be regarded as an alternative to it. 
On the broad issue we think the verdict must be that this 
department should be handed over to the laboratory physiologist 
for that intensive analytical study which Dr. Clements deplores 
before the synthetic treatment of these correlations which we all 
desire becomes possible. 
Factors of the Habitat. 
From this consideration of the foundations of the correlation 
between habitat and plant we may pass to Dr. Clements’ treatment 
of each of them separately. 
Dr. Clements opens his chapter on “The Habitat” by defining it 
as the sum of all the factors in the environment. In the first class 
of importance he places three, to wit, water content of soil, humidity 
of the air, and light. These are the differentiating factors between 
habitats and on them the qualitative structural differences of ecads 
depend. As a factor, temperature is of great importance, 
naturally, but differences of temperature are regarded as only causing 
quantitative structural effect not qualitative differences and so are 
not further considered. 
Dr. Clements’ ideal is to obtain abundant measurements, or 
where possible, continuous records by automatic instruments as to 
all these and other factors, separately, so that the habitat may be 
definable in exact quantitative terms. It is expected that finally 
there will come out a correlation between the means or the sums of 
the intensities of these various factors (stimuli of Dr. Clements) 
during the vegetative period and the various functional activities 
and structural modifications of the plant. 
We may briefly mention the methods proposed by Dr. Clements 
