H2 ROBERT SMITH [February 



(1) The constitution of each species, some being able to crush out 

 their neighbours in virtue of certain characteristics such as rapid 

 growth, long duration, quick germination, shade, etc. 



(2) The particular conditions of each station. He remarks, too, 

 how many species have the social habit, even to the limits of their 

 area of distribution, where they disappear suddenly and new forms 

 take their place. He reasons that purely local causes seem to be 

 of much more importance than general climatic conditions in 

 determining the abundance of the individuals of a species at any 

 particular point. It is owing to this fact that the study of social 

 species is valuable in topographical botany. He also calls attention, 

 as Humboldt had done before, to the difference between such a case 

 as that of a northern pine forest, where one species is dominant, even 

 to the exclusion of others, and such a case as a tropical forest, 

 where a certain normal character is given by a mixture of many 

 associated species. 



Thus the scope of the subject had been foreseen and discussed by 

 the middle of the century, but as yet its interest was almost purely 

 geographical, and the biological element was hardly touched upon. 



With Darwin a new period in natural science began. He directed 

 attention upon organisms in nature, how they are adapted to their life, 

 and how they struggle for existence. Since 1859 a steady stream of 

 works have appeared treating of the anatomical and physiological 

 characters of plants in relation to their habitat. In the bibliography 

 at the end of this paper a few only of the chief of these have been 

 mentioned as representative oecological works, dealing with such marked 

 forms of vegetation as strand plants, acuiatic plants, halophytes, desert 

 plants, etc. (see List B). Such close associations as exist between 

 symbions, and between parasites, epiphytes, and climbing plants and 

 their hosts, have already an extensive literature devoted to them. The 

 associations of plants and animals, especially plants and insects, have 

 occupied the time of many investigators, even to the neglect of the 

 more general study of plant association. 



The first to apply the new ideas to the description of the vegeta- 

 tion of a particular region was Kerner (1863) in his work on the 

 plant-life of the basin of the Danube. After describing the general 

 characters of the region, he represents the vegetation as being made 

 up of a number of " formations " (as defined by Grisebach), each 

 " formation " characterised by some definite species (one or more), 

 possessing adaptations which enable it to suit the particular conditions 

 of environment and to dominate in the landscape. Thus the first steps 

 of the method were : — 



(1) To describe the general characters of vegetation. 



(2) To enumerate the leading plant "formations" of the region 



and the plants which dominate in each. 



