488 ECOLOGY 



the heart as the seat of the emotions, and of the rising and the setting 

 of the sun, so it is likely that some teleological expressions remain. 

 Some words of which frequent use is made, such as advantage or efficient, 

 may to some appear teleological. Such terms, however, are employed in 

 the sense of the perpetuity of the species. Any structure or reaction 

 that favors the extended duration of an individual or of the race to which 

 it belongs is regarded as advantageous, whil : any structure or reaction 

 that is detrimental to such duration is regarded as disadvantageous. In 

 this sense such a word as advantage is not teleological, for it might be 

 thus employed with reference to many inorganic substances. 



The arrangement of the material. In the following pages the ma- 

 terial is grouped on the basis of structure, the fundamental plant parts 

 being regarded as roots, leaves, stems, and reproductive organs. The 

 same material might be grouped under the head of behavior, includ- 

 ing such topics as absorption, conduction, synthesis, transpiration, 

 reproduction, and the like; or again, the material might be grouped 

 under the head of factors, as light, heat, water, etc. The method here 

 used, that of classification by structure, seems best suited to the present 

 state of ecological knowledge, where structure alone is approximately 

 sure. In many cases, organs have no known r61e, and still more fre- 

 quently a given organ has two or more rdles, thus making a classi- 

 fication by behavior difficult and repetitious; furthermore, classification 

 by behavior places too much emphasis upon the employment of organs 

 and is likely to lead to teleological mysticism. The classification of 

 ecological data by factors is fundamentally sound, but is at present 

 practically impossible, owing to the paucity of known facts as compared 

 with those that are unknown. 



The differentiation of the plant body. While the material here pre- 

 sented is classified chiefly under roots, leaves, stems, and reproductive 

 organs, it is not assumed that there are hard and fast lines between 

 these plant parts. The evolutionary hypothesis presupposes transitions 

 between all organs, and there are many evidences of intergradations 

 even between the most diverse plant parts. In the lowest plants the 

 body is an undifferentiated thallus. In algae and fungi there is seen 

 the first conspicuous differentiation, that between vegetative and re- 

 productive organs. In the thallose liverworts the vegetative part be- 

 comes differentiated into a green food-making aerial portion and a 

 colorless rootlike subterranean portion; in the leafy liverworts and in 

 mosses the aerial vegetative portion is differentiated still further into 



