ECOLOGY

the study of the adjustment and response of plants and plant communities to various environmental factors, those being on the one hand climatic or geographical and atmospheric and on the other edaphic—that is, concerned with soil characters. Warming has recently cla ified the atmospheric (a) and edaphic factors () as follows: (a) light, temperature, atmospheric humidity and precipitations, movements of the air; (6) the nutrient substratum, its constitution, structure, air, water, temerature, dimensions and nutriment, the Einds of soil, the problem as to the chemical or physical action of soil. Under the influence of these and certain other factors plants fall into thirteen ecological cla es, viz.: Hydrophytes, purely aquatic including plankton and marine floras, and the submerged vegetation of lakes, etc.; Helophytes, marsh formations, including tropical swamps; Ozylophytes, on acid soils such as peat; Psychrophytes, on cold soils such as tundras; Halophytes, saline soil formations; Lithohytes, rock formations such as lichens; Racniiaphytes, formations of sand dunes and the like; Cher sophy tes, waste land formations; Eremophytes, desert and nas; Sclerophyllows formations, Mediterranean maqul, karroo; Coniferous forests; Mesophytes, meadow and forest of tem- ‘aba climes living under average contions without great extremes.