ESSENTIALS OF A SYSTEM 17 



lo all others is ihe one that exists between the habitat and the plant. This 

 relation has long been known, but its full value has yet to be appreciated. 

 It is precisely the relation that exists between cause and effect, and its fun- 

 damental importance lies in the fact that all questions concerning the plant 

 lead back to it ultimately. Other relations are important, but no other is 

 paramount, or able to serve as the basis of ecology. Ecology sums up this 

 relation of cause and effect in a single word, and it may be that this ad- 

 vantage will finally cause its general acceptance as the proper name for 

 this great field. 



In the further analysis of the connection between the habitat and the plant, 

 it is evident that the causes or factors of the habitat act directly upon the 

 plant as an individual, and at the same time upon plants as groups of in- 

 dividuals. The latter in no wise decreases the importance of the plant as 

 the primary effect of the habitat, but it gives form to research by making it 

 possible to consider two great natural groups of phenomena, each character- 

 ized by very different categories of effects. Ecology thus falls naturally 

 into three great fundamental fields of inquiry : habitat, plant, and formation 

 (or vegetation). To be sure, theMast can be approached only through the 

 plant, but as the latter is not an individual, but the unit of a complex from 

 the formational standpoint, the formation itself may be regarded as a sort 

 of multiple organism, which is in many ways at least a direct effect of the 

 habitat. In emphasizing this fundamental relation of habitat and vegeta- 

 tion, it is imperative not to ignore the fact that neither plant nor formation 

 is altogether the effect of its present habitat. A third element must always 

 be considered, namely, the historical fact, by which is meant the ancestral 

 structure. Upon analysis, however, this is in its turn found to be the product 

 of antecedent habitats, and in consequence the essential connection between 

 the habitat and the plant is seen to be absolute. 



26. The place of function. In the foregoing it is understood that the 

 im.mediate effect of the physical factors of the habitat is to be found in the 

 functions of the plant, and that these determine the plant structure. Func- 

 tion has so long been the especial theme of plant physiology that methods 

 of investigation are numerous and well known, and it is unnecessary here 

 to consider it further than to indicate its general bearing. The essential 

 sequence in ecological research, then, is the one already indicated, viz., 

 habitat, plant, and formation, and this will constitute the order of treatment 

 in the following pages. That portion of floristic which is not mere de- 

 scriptive botany belongs to the consideration of the formation, and in con- 

 sequence there will be no special treatment of floristic as a subdivision of 

 ecology. 



