xiv A. F. W. SCHIMPER 



But observation further shows that in the same environment 

 many of the plants not possessing the common features above 

 mentioned yet have characters subserving the same end, so that 

 they as well as the first group are machines having one common 

 object, that of working in harmony with the dominant factor. 

 Consequently, comparative observations upon the various members 

 of one community or guild of plants afford another method of 

 investigation. This is brought out vividly in Schimper's papers 

 on epiphytes and littoral plants, where the various mechanisms 

 are described by which water is stored or economized by leaves, 

 stems, or roots. One admirable example is specially given in the 

 form of a comparison between the structure of the two epiphytes, 

 Tillandsia usneoides, composed solely of shoots, and an Aerantkus, 

 whose vegetative organs consist entirely of green roots. 



But further morphological and histological examination of 

 members of the same community or guild may reveal the exist- 

 ence of some apparently devoid of any peculiar structural features 

 fitting them for their special mode of life. An investigation into 

 their physiology and mode of life may at once show that they are 

 really not under the control of the dominant factor, or like ephe- 

 merals in the desert evade it by the periodicity of their life, though 

 their environment may appear at first sight to be all but identical 

 with that of their elaborately adapted neighbours. This lack of 

 need for working in harmony with the dominant factor affords 

 a third means of testing the conclusions previously arrived at in 

 reference to the other plants. Thus Schimper pointed out the 

 existence of many epiphytes which are not xerophytic, but may 

 even be hygrophytic in structure, and he further correlated this with 

 the fact that these particular plants exist as epiphytes only on very 

 moist and shady parts of tree-trunks, and consequently require no 

 careful provision against excessive transpiration. 



Having thus demonstrated the intimate and necessary relation 

 between the structure of the plants and the dominant factor, the 

 next work nwht be an investigation into the extent to which the 

 peculiar structure of the plant is the direct result of the environ- 

 ment. This matter Schimper scarcely touched, except in the case 

 of halophytes, where he cited the observations of others and 

 recorded his own. 



