THE PROBLEMS OF ECOLOGY 193 



on this subject are apt to leave the reader a little in doubt whether 

 ecology is to be regarded as a phase or subdivision of plant geo- 

 graphy, or whether plant geography is only a generalized form of 

 ecology, or finally whether the two are capable of separation even 

 by a rather vague boundary. So much, however, may be said with 

 definiteness. These branches of botany have arisen independently 

 and differed greatly in their history and point of view. They have 

 both dealt with adaptation of plants to conditions of soil, climate, 

 and communal life, but have approached the subject from opposite 

 sides. Plant geography, much the older of the two subjects, was 

 at first closely allied to systematic botany. It was pursued chiefly 

 by systematists, and consisted largely of a series of generalizations 

 upon the distribution of genera and species and their rough group- 

 ing into floras. More and more has the plant geographer studied the 

 adaptive traits of plants, and observed their biological rather than 

 their systematic relationships, until he now bases most of his con- 

 clusions upon ecological data. On the other hand, the ecologist, 

 beginning with the individual plant and examining the relation of 

 its structure to its activities and the activities to the environment, 

 has been gradually and naturally led to wider and wider general- 

 ization regarding the influence of structure upon distribution and 

 of environment upon structure, until in his plant societies and 

 plant formations, he has speedily arrived by another path at just 

 the point more slowly reached by the plant geographer. 



The material of these two branches of botany is nearly or quite 

 coextensive. It is difficult to find any ecological modification of 

 a plant which is not at least in some slight way connected with its 

 distribution, and conversely the present distribution of plant life, 

 which forms the subject-matter of plant geography, has undoubtedly 

 resulted immediately or remotely from ecological causes. It has been 

 well said that plant geography is the study of the present conse- 

 quences of past ecological conditions. 



By its nature plant geography has been descriptive and classi- 

 ficatory. With all due regard to their natural affinities, adaptation, 

 and gradual association, it has grouped plants primarily according 

 to the soil and climatic conditions in which they grow. Ecology deals 

 with the dynamics of plant life, with such phenomena as competition 

 among plants, crowding and tension of floras, migration of plants, 

 parasitism, symbiosis, and the complex relations of benefit and 

 injury which exist between plants and animals. It is of all depart- 

 ments of botany the most recent in development, rapid in growth, 

 and fascinating in subject-matter. The details of classification, ana- 

 tomy, and physiology are dry and cold compared with such ecological 

 discoveries as the varied modes in which plants are protected against 

 the attacks of animals, the complicated ways in which they scatter 



