l8] PLANT ADJUSTMENTS AND APPLICATIONS 577 



in connection with human and domestic animals' diseases, so many 

 of which are caused by Bacteria. 



In wildhfe management the most effective activity for increasing 

 numbers is often improvement of the habitat, and in fresh waters 

 the effect of adding fertilizer or manure (as in European carp-ponds) 

 may be remarkable. The same can be true in salt waters, as was 

 demonstrated during World War II in Scottish fiords where the 

 addition of nutrients led to the extraordinarily rapid growth of Plaice 

 and other Fishes. Many agricultural, horticultural, and forestral 

 practices are comparable with this to the extent that the habitat is 

 commonly prepared for some particular crop or other plant — which 

 is usually an exotic form and, very often, unable to persist without 

 the maintenance of some special man-made habitat. With this 

 principle of habitat preparation and maintenance, with cultivation and 

 tillage, we are already familiar ; but it should be re-emphasized 

 here as it is largely applicational and, moreover, can and does lead 

 to vast extensions in the ranges — albeit artificial — of many plants. 

 As an extreme case Man is able, with the knowledge born of sufficient 

 experimentation, to create in the laboratory or greenhouse almost 

 any environment anywhere, so long as he cares to pay the necessary 

 price. 



Particular plants or vegetation-types often give a useful indication 

 of the geological substrata on which they grow. For example, faults 

 in various rocks or different strata of sandstone can exhibit marked 

 fioristic or vegetational differences. This may extend to questions 

 of presence or absence of valuable minerals and, where no other 

 than fioristic or vegetational changes are visible at the surface, may 

 be of obvious use in prospecting. In general, however, this subject 

 has been little stressed except in particular instances and places, so 

 that the field lies wide open for more precise observation and 

 application. 



Of indicator plants — or, better, groups of plants — there are many 

 that can be valuable for agricultural or other planning. Examples 

 include the Cacti and ' desert ' shrubs that indicate overgrazing in 

 many parts of the American southwest, or the Sheep Sorrel and 

 other small weeds that indicate a similar condition in many cool- 

 temperate areas. Further indicators of similar or other conditions 

 are mentioned in almost any modern ecological or allied text-book, 

 and especially in the works of Clements cited at the end of this 

 chapter. Indeed, most of the important habitat conditions have 

 their plant indicators, even though we may not think of them 



