GEOGRAPHIC DISTRIBUTION OF SEED-BEARING PLANTS. 



This is one of the most difficult and im- 

 portant subjects connected with the study 

 of plants. Before it can be well organized 

 it will be necessary to bring together very 

 many more observations of plants in. all 

 parts of the world than is possible now. 

 However, a few facts are known which 

 are both interesting and suggestive. In 

 order to make their presentation as defin- 

 ite as possible, this paper will be restrict- 

 ed to a brief account of the geographic 

 distribution of seed plants. 



One of the two great groups of seed 

 plants is known as the Gymnosperms, a 

 group which in our region is represented 

 by pines, spruces, hemlocks, cedars, etc. 

 In the tropics the group is represented 

 by a very difTerent type of trees, known 

 as the Cycads. They resemble in gen- 

 eral habit tree-ferns, or palms. The group 

 of Gymnosperms with which we are ac- 

 quainted have been called Conifers on 

 account of the very characteristic cones 

 which they bear. Several principles con- 

 nected with geographic distribution may 

 ])e illustrated by considering briefly these 

 two groups of Gymnosperms. 



The Cycads are absolutely restricted to 

 the tropics, a few forms reaching into 

 semi-tropical conditions, as in southern 

 Florida. If a comparison be made be- 

 tween the eastern and western tropics, it 

 will be discovered that the Cycads are 

 almost equally divided 1)ctween the two 

 regions. For an unknown time, but cer- 

 tainly a very long one, these eastern and 

 western Cycads have been separated from 

 one another. As a consequence they have 

 l)ecomc so unlike that one kind of Cycad 

 is never found in both hcmis])heres. 

 Tlieir long separation from one another, 

 and their somewhat (hfTerent conditions 

 of living, have resulted in working out 

 differences of structures wliicli botanists 

 recognize as species, genera, etc. 



The Conifers, on the other hand, are 

 characteristic of temperate regions. If 

 the distribution of Conifers were indicated 

 upon a world map, there would be shown 

 a heavy massing of them in the northern 

 region and a lighter massing in the south- 

 ern region, the two being separated from 

 one another by a broad tropical belt. This 

 tropical belt is traversed in just two 

 places ; one is by means of the East In- 

 dian bridge, across which certain Aus- 

 tralasian forms reach China and Japan ; 

 the other is the chain of the Andes moun- 

 tains, along which a single northern type 

 has worked its way into the southern part 

 of South America. The two great masses 

 of Conifers, therefore, lie in the northern 

 and southern hemispheres, rather than 

 in the eastern and western hemispheres, 

 as is the case with the Cycads. This long 

 separation has resulted just as it did with 

 the Cycads ; that is, the northern and 

 southern Conifers are not any longer 

 alike, but differ so widely from one an- 

 other that botanists cannot discover any 

 form which is common to both the north- 

 ern and southern hemispheres, excepting 

 the single one already mentioned, w^hich 

 has succeeded in crossing the tropics by 

 means of the Andes bridge. 



Another interesting fact in connection 

 with the distribution of the Conifers is 

 that their great centers of display are in 

 regions which border the Pacific Ocean, 

 and they have often been spoken of as a 

 Pacific group. There are three special 

 centers of display ; one is the China-Japan 

 region, a second is the general Australa- 

 sian region, and the third is western 

 North America. Just why this border re- 

 gion of the Pacific is especially favorable 

 for this sort of plant life is a (juestion 

 which we do not as yet pretend to answer. 

 Anotlier fact which illustrates this per- 

 sistent (listributicMt in connection with 



