INTRODUCTION. 285 



qualities. By a study of the life histories of plants, their habits 

 and behavior under different conditions of environment, we 

 shall broaden our concept of nature and cultivate our aesthetic, 

 observational, and reasoning faculties. The subject is too 

 large for full treatment within the limits of a part of an elemen- 

 tary book. The way here can only be pointed out, and the few 

 examples and illustrations, it is hoped, will serve to open the 

 book of nature to the young student, and lead him to study 

 some of the problems which are presented by every region. 

 This study of plants, in their mutual and environmental rela- 

 tionships, is ecology. 



453. Some of the factors of environment. — In carrying on 

 studies of this kind one should bear in mind the factors which 

 influence plants in these relationships, that is, what are called 

 the ecologic factors ; in other words, those agencies which make 

 up the environmental conditions of plants, all of which play a 

 greater or lesser role in the habit or status of the plant con- 

 cerned, and which, acting on all plants concerned, give the 

 peculiar color or physiognomy to the plants of a region or of a 

 more restricted community. 



Such factors are climate, with its modifying meteorological 

 conditions; texture, chemistry, moisture content, covering, 

 topography, exposure, etc., of the soil; influence of light and 

 heat; of animals, of plants themselves, and so on. 



454. Suggestions for outdoor studies. — For beginning 

 classes, where only a small part of the time is available, excur- 

 sions can be made from time to time during the year for this 

 purpose, taking certain subjects for each excursion. For 

 example, in the autumn one may study means for the dissemi- 

 nation of seeds, protection of seeds, plant formations, zonal 

 distribution of plants, formation of early spring flowers, etc. ; 

 in the winter, twigs and buds, protection of plants against the 

 cold; and in the spring, opening of the buds and flowers, 

 pollination, etc., and further studies on plant societies, relation 

 of plants to soil, topography, etc. 



