AN API'RPXIATION xiii 



An analysis of Schimper's oecological methods may therefore 

 be of interest. 



To explain how plants are fitted to subsist in the precise 

 environment that they occupy demands an elaborate inquiry 

 into the form, structure, physiology, and life-history of the 

 plants, and an equally exhaustive analysis of their animate and 

 inanimate surroundings. But to solve the still further problem 

 as to the original source and evolution of the plants and of 

 the whole community, necessitates a corresponding investigation 

 relating to the immediate allies of these plants living under other 

 conditions. 



Such an exhaustive oecological research is at present only 

 theoretically possible, and it is practicable only to get definite 

 answers to our questions by an investigation of one or more 

 dominant factors which impress themselves strongly on the forms 

 and behaviour of the plants under their influence. Such dominant 

 factors we may consider insects in relation to flowers, and drought 

 in relation to desert plants. Schimper always worked with plants 

 under the influence of some such dominant factor. In all his 

 oecological papers, save one on myrmecophilous plants and two 

 short earl)- papers, the dominant factor under which the in- 

 vestigated plants (epiphytes, alpine and littoral plants, halophytes) 

 lived was scarcity of available water. 



Such a dominant factor, in impressing itself on the form of 

 the plants, will lead to the occurrence of some structural feature 

 or features common to all or to many of the plants. In fact, in 

 ordinarj- work it may be that these features, in largely determining 

 the facies of the vegetation, first suggest the existence of a domi- 

 nant factor. The first obligation is to prove that these features 

 are absolutely necessary, or at least highly advantageous, to the 

 plants possessing them. Physiological experiments or observa- 

 tions on the life-history of the plants alone can give this proof. 

 It was thus that Schimper showed the xerophilous nature of the 

 leaves of epiphytes, halophytes, and alpine plants, which dwell in 

 physiologically dry places, whether the physiological drought be 

 due to scanty supply of water, or to unavailability of the water 

 by reason of its salinity, or to external influences promoting 

 transpiration. 



