MODERN BIOLOGY 561 



with plant communities, by which is meant plants of very different systemati- 

 cal categories that, on account of a uniformity in the alimental conditions, 

 have adapted themselves to living together within a certain area. The aim 

 of this tendency is to analyse such plant-associations and to ascertain their 

 relations to the climate, the soil, and other environmental conditions. Both 

 these tendencies have made considerable progress up to recent times and can 

 claim a number of distinguished representatives, of whom it is possible only 

 to name a few. The two previously mentioned English botanists Brown and 

 Hooker made valuable observations as to the distribution of plants, espe- 

 cially in extra-European countries. The Swiss Oswald Heer (1809-83) made 

 a special study of the conditions of the flora of the glacial period and also 

 of earlier geological strata. There followed in his tracks the Swede Alfred 

 Nathorst (i850-i91x), who did very creditable work in investigating the 

 fossil vegetable world of the polar countries. Adolf Engler (born in 

 1844), professor at Berlin and founder of an important school of plant 

 geography, has endeavoured, by studying the recent and fossil vegetable 

 world, to gain some insight into the evolution and changes of the flora, espe- 

 cially in the temperate countries. August Heinrich Grisebach (1814-79), 

 professor at Gottingen, sought to carry out an investigation into the influ- 

 ence of climate on the vegetation and a classification, on a climatic basis, 

 of the flora in certain areas. The Dane Eugen Warming (1841-19x4) per- 

 formed a considerable service to science by his study of plant-associations, 

 which he classified and analysed in respect of plant forms and conditions 

 of life. By this work he made a contribution to oecological plant-geography 

 of fundamental importance. Andreas Franz Wilhelm Schimper(i856-i9oi), 

 professor at Basel, made long voyages for the purpose of studying tropical 

 vegetation, and from climatological and modern physiological points of view 

 he worked out the vegetation of the entire globe in his Vjianxengeogra-phie 

 auf fhysiologischer Grundlage (1898). His geographical and oecological classi- 

 fications have exerted great influence upon subsequent development. 



