384 Forestry Quarterly 



the systematic botanists of the ancients. These men studied the 

 distribution of plants over the then known world. This phase 

 of plant geography flourished greatly when explorations and mili- 

 tary conquests opened up new and unknown parts of the globe. 

 Since the middle ages the study of vegetation as a whole and 

 the various climatic and geographic units of which it is made up 

 claim the attention of plant geographers. This study naturally was 

 the outcome of the purely taxonomic study of plant distribution 

 that preceded it. The corner-stone of plant ecology was laid in the 

 beginning of the 19th century, when the plant formation was 

 recognized as the fundamental unit of vegetation. Historically 

 speaking, therefore, this event may be taken as the dividing line 

 between plant geography and plant ecology, but this does not 

 mean that the two are separable into distinct sciences. In its 

 broadest sense plant geography includes plant ecology, the latter 

 being merely the latest stage in the development of the former. 

 From our point of view, therefore, it is neither necessary nor de- 

 sirable to speak of their historical development separately. 



Plant geography is usually defined as the science dealing with 

 the geographical distribution of plants over the earth's surface 

 both past and present. The problem of plant distribution presents 

 a twofold aspect : it has, first, to map out the surface of the earth 

 into "districts" or other "areas of vegetation" and, secondly, to 

 investigate the causes which brought them about and have led to 

 their restriction and to their mutual relations. The complexity of 

 this science is due to the intricacy of geographical and geological 

 evolution. If the surface of the earth were of the same eleva- 

 tion all over, and if it had been symmetrically divided into land 

 and sea and these had been evenly distributed in bands parallel 

 to the equator, the character of the earth's vegetation would de- 

 pend practically upon temperature alone and the study of plant 

 distribution would be a comparatively simple matter. But land 

 and sea are distributed in an extremely irregular way, and within 

 each of the earth's temperature zones there is the great local 

 diversity of moisture, elevation, and isolation, with correspond- 

 ingly great variations in vegetation. 



Warming (15) subdivides plant geography into floristic plant 

 geography and ecological plant geography. The former deals 

 with the division of the earth's surface into major districts 

 characterized by particular plants or taxonomic groups of plants. 



