AN APPRECIATION xv 



Much more attention he devoted to the adaptive nature of 

 structural peculiarities fitting- the plants for their mode of life. 

 He asked whether particular peculiarities of a plant were truly 

 adaptive, that is, whether they had been evolved for the specific 

 purpose of enabling- the plant to exist in its present surroundings, 

 or to what extent they were previously possessed by the plant, 

 thus enabling it to enter its present home. This entailed an 

 investigation into the structure of allied plants living under other 

 surroundings. As examples of such comparative investigations 

 may be cited Schimper's discussions on the velamen of orchids 

 and aroids, on vivipary in mangrove-plants, on mechanisms of 

 seed-dispersal of littoral plants, and in particular on the evolution 

 of floating tissue, which he investigated by comparisons between 

 the fruits of inland and littoral species of one genus. His investi- 

 gation of the myrmecophilous Cecropia is an excellent example of 

 this method. Having demonstrated the necessity of the protec- 

 tion against leaf-cutting ants, and having recalled known facts, that 

 the Cecropia supplies food and home to the protecting army of 

 ants, Schimper rendered probable the adaptive nature of the 

 food-bodies by showing their composition and behaviour, and their 

 absence in a non-myrmecophilous species of Cecropia likewise 

 growing in Brazil ; and by a further comparison of the two species 

 he also showed that there was a definite structural adaptation 

 for facilitating the entrance of the protective ants into the hollow 

 internodes of the myrmecophilous plant. 



Change in the environment occasions change in the composi- 

 tion and oecology of the vegetation. There is thus between the 

 oecology and the geographical distribution of plants a reciprocal 

 relation which renders observations on either of these subjects 

 helpful in the explanation of the other. 



Observations on the local distribution of types of vegetation, 

 in that they deal with variations of environment associated with 

 little or no change in climate, frequently render possible the recog- 

 nition of the factors determining- the original formation of definite 

 communities of plants, and the analysis of the primary and some 

 of the secondary factors influencing the structure of the consti- 

 tuent plants. It was by observations on the local distribution of 

 epiphytes in the American tropics that Schimper was able to 



