l8] PLANT ADJUSTMENTS AND APPLICATIONS 571 



has already gone, and that the water-cycle has been drastically 

 disturbed. This is a most distressing situation to which Professor 

 Paul B. Sears's book Deserts on the March drew eloquent attention 

 more than two decades ago. Conservation of soil and other natural 

 resources is above all a way of life, as people have come more and 

 more widely to realize in recent years, though still there is not nearly 

 enough appreciation of its significance, let alone application of 

 effective measures. 



Plant Geographical Study 



A plant geographer should have considerable knowledge of ecology 

 on one hand and of taxonomy on the other. His work must be 

 ecologically based in its analysis of environmental factors as an 

 outcome of which he can tell, for example, why such and such a 

 plant community is restricted to such and such an area ; and above 

 all it must rest upon a sufficiently precise taxonomy. Those are 

 the immediate prerequisites of plant geographical study. For sound 

 ecological knowledge some understanding of a wide range of basic 

 sciences even outside of biology is necessary ; as for precise 

 taxonomy, even closely allied and superficially similar plants can 

 have very different reactions to environmental conditions, and so a 

 knowledge of the local flora in the particular area of interest is 

 virtually essential. 



The methods of the modern plant geographer must accordingly 

 be as scientifically based and exact as is humanly possible. Admit- 

 tedly a good deal may be done by merely determining what grows 

 where. For this the main requisite, apart from intensive field 

 investigation, is to know precisely what we are dealing with — namely, 

 the identity of each particular plant in question, coupled with the 

 ability to determine that it is essentially the same ' kind ' throughout 

 the ascertained range. But for interpretation and application of 

 such observations we must have far wider knowledge and biological 

 understanding — or, instead, an empirical system which could scarcely 

 be worked out in sufficient detail for general use. 



The ecological reactions of closely-related species or even races 

 of plants can vary markedly, as can, accordingly, their ranges both 

 individually and as components of vegetation, so the plant geographer 

 must be able to recognize both habitat and taxonomic differences. 

 For such ecological items his knowledge of soils and climates and 

 of their component factors is particularly important, while as tools 



