178 
Review : 
matter which he has felt compelled to insert—matter, we mean, 
which can only be held to be ecological when such a broad view is 
taken of ecology that the term ceases to possess any precise or 
definitive significance. In short, whilst it is self-evident that 
physiology and ecology have much in common, and that many 
physiological experiments should be conducted in the field, we do 
not believe that it is in the interests of either of these branches of 
botany to blend, at the present juncture, a text-book of physiology 
and one of ecology. We should, however, welcome a text-book 
which dealt with ecology from the physiological point of view, and 
which was written for students who had already received some 
training in the methods of plant physiology. 
In studying the various factors of the habitat, the methods put 
forward by Professor Clements are essentially quantitative. Such 
a plan is excellent so long as the right things are measured, but this 
cannot be said of all the quantitative methods detailed in the book. 
For example, the method of obtaining soil-samples (p. 10) gives no 
guarantee that the soil examined is the soil being put to use by the 
plant which is being investigated. It may be admitted that 
practically all agriculturists make the same mistake. Soil analyses 
rarely, if ever, take into account the facts that different species of 
plants utilize different layers of soil, and that these different layers 
of soil possess different water-contents and different mineral-contents. 
An analysis of “ a soil ” is not of much consequence; what matters 
is an analysis of that part of the soil in which the roots of the plants 
are functioning. 
Again, in determining the amount of available water in the soil, 
the whole method turns on the recognition of the time “ when the 
plant wilts completely.” Such a determination is not difficult in the 
case of plants with thin deciduous leaves which contain much water, 
such as Helianthemum and Dahlia ; but it is more than difficult, it 
is impossible, in the case of many plants with small, dry, evergreen 
leaves such as Calluna and Erica, which die before they wilt. Even 
in the case of some plants with thin deciduous leaves, after the 
leaves have wilted completely, the work of transpiration and 
assimilation is continued by the young shoots, as in Vaccinium 
Myrtillus. In all such cases, and perhaps also in the case of such 
plants as Sedum with succulent leaves, the method of Professor 
Clements breaks down. Generally, we think that a number of the 
quantitative experiments here outlined possess only a <7?msi-exactness 
which however may deceive the unscientific. 
