CHAPTER XIII 



GEOGRAPHIC DISTRIBUTION OF ANGIOSPERMS 



So vast a subject can be presented only in very brief outline 

 in a single chapter. In a certain sense it is not pertinent to 

 a discussion of the special morphology of a group, but the stu- 

 dent of special morphology is aided by certain general consid- 

 erations connected with geographic distribution, especially in 

 any discussion of phylogeny. The distribution of a group con- 

 taining nearly 125,000 species includes a vast mass of details, 

 and only certain salient features can be selected for presenta- 

 tion. Even when these are selected, the numerous exceptions 

 to anv general statement must be disregarded. It must be un- 

 derstood, therefore, that in the following account the statements 

 are very general in their nature, expressing average conditions 

 of distribution, under all of which exceptions may be cited. 

 At the same time, it is the general tendency in the distribution 

 of any large group that is of interest to the morphologist rather 

 than the details of distribution of species and genera. 



The subject of geographic distribution presents two aspects 

 for consideration. One involves the determination of life-zones 

 over the surface of the earth, which is a consideration of dis- 

 tribution from the standpoint of physiography. The other 

 aspect disregards the life-zones, and considers distribution from 

 the standpoint of plant-groups. What a given plant-group has 

 been able to do in the occupation of the earth's surface is of 

 more morphological interest than the physiographic features 

 of the problem, and hence the following presentation will take 

 the latter standpoint. 



Including only the existing vegetation gives a very inade- 

 quate conception of the relation of any group to the earth's 

 surface. The present distribution of a group is only the last 



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