GEOGRAPHIC DISTRIBUTION OF SEED-BEARING PLANTS. 



This is one of the most difficult and im- The Conifers, on the other hand, are 



portant subjects connected with the study characteristic of temperate regions. If 



of plants. Before it can be well organized the distribution of Conifers were indicated 



it will be necessary to bring together very upon a world map, there would be shown 



many more observations of plants in all a heavy massing of them in the northern 



parts of the world than is possible now. region and a lighter massing in the $out! 



However, a few facts are known which ern region, the two being separated from 



are both interesting and suggestive. In one another by a broad tropical belt. This 



order to make their presentation as defin- tropical belt is traversed in just two 



ite as possible, this paper will be restrict- places ; one is by means of the East In- 



ed to a brief account of the geographic' dian bridge, across which certain Aus- 



distribution of seed plants. tralasian forms reach China and Japan ; 



One of the two great groups of seed the other is the chain of the Andes moun- 

 plants is known as the Gymnosperms, a tains, along which a single northern type 

 group which in our region is represented has worked its way into the southern part 

 by pines, spruces, hemlocks, cedars, etc. of South America. The two great masses 

 In the tropics the group is represented of Conifers, therefore, lie in the northern 

 by a very different type of trees, known and southern hemispheres, rather than 

 as the Cycads. They resemble in gen- in the eastern and western hemispheres, 

 eral habit tree-ferns, or palms. The group as is the case with the Cycads. This long 

 of Gymnosperms with which we are ac- separation has resulted just as it did with 

 quainted have been called Conifers on the Cycads; that is, the northern and 

 account of the very characteristic cones southern Conifers are not any longer 

 which they bear. Several principles con- alike, but differ so widely from one an- 

 nected with geographic distribution may other that botanists cannot discover any 

 be illustrated by considering briefly these form which is common to both the north- 

 two groups of Gymnosperms. ern and southern hemispheres, excepting 



The Cycads are absolutely restricted to the single one already mentioned, which 



the tropics, a few forms reaching into has succeeded in crossing the tropics by 



semi-tropical conditions, as in southern means of the Andes bridge. 



Florida. If a comparison be made be- Another interesting fact in connection 



tween the eastern and western tropics, it with the distribution of the Conifers is 



will be discovered that the Cycads are that their great centers of display are in 



almost equally divided between the two regions which border the Pacific Ocean, 



regions. For an unknown time, but cer- and they have often been spoken of as a 



tainly a very long one, these eastern and Pacific group. There are three special 



western Cycads have been separated from centers of display ; one is the China- Japan 



one another. As a consequence they have region, a second is the general Australa- 



become so unlike that one kind of Cycad sian region, and the third is western 



is never found in both hemispheres. North America. Just why this border re- 



Their long separation from one another, gion of the Pacific is especially favorable 



and their somewhat different conditions for this sort of plant life is a question 



of living, have resulted in working out which we do not as yet pretend to answer, 



differences of structures which botanists Another fact which illustrates this per- 



recognize as species, genera, etc. sistent distribution in connection with 



42 



