Aspects of Ecology. 
243 
just that amount corresponding to the C0 2 diffusing in from 
outside (which depends on the porosity of the leaf), plus the 
C0 2 produced inside in respiration. These values can only be 
obtained by experiment and, till known, we cannot be said to know 
the light-factor of the habitat from the point of view of photo¬ 
synthesis. If the intensity of the factor is not critically known 
how can structure (especially until its functional mechanism is fully 
understood) be correlated with it quantitatively ? What seems to 
be next wanted is critical analytical experimental work combining 
laboratory methods with field conditions in order that the 
fundamental principles of these correlations in Nature may be 
worked out. Each plant of a given habitat may prove to be a 
different equation to the same final value, that of the habitat, and 
it may well be thought that the functional significance of the 
factors must be worked out before anything more can be got out of 
the formation from this point of view than will be revealed to acute 
observation without measurement. 
Methods of Vegetation Analysis. 
In his fourth chapter, “The Plant Formation,” Dr. Clements 
passes to the methods of proximate analysis of the phenomena of 
vegetation, in other words to Phytotopography proper. At the 
outset he insists on the need of exact methods, and puts forward 
the “quadrat-chart” as the basis of investigation. A “quadrat” is 
simply a square area of convenient size marked off in a plant 
formation for the purpose of analysis, and the “quadrat-chart” is 
a record of the vegetation on the quadrat in the form of a map on 
which the position of each individual plant is recorded. 
The quadrat-chart may be regarded as a fundamental instru¬ 
ment in the study of the formation, and, together with allied 
methods, furnishes the only means of obtaining detailed and 
accurate information of the minute structure of vegetation. Among 
the more immediate uses of such information are, the possibility it 
gives of exactly comparing the structure and composition of different 
parts of the same formation, and of similar formations in different 
localities, the means it furnishes of ascertaining exactly the amount 
of change in any given formation from year to year, and especially 
the possibility of accurately tracing the successive stages in the 
development of vegetation on new and denuded soils. Of its 
ultimate uses it need only be said that the quadrat-chart will form 
