BOOKS AND LITERATURE 279 



Draha. The great variability of species of this genus and 

 the impracticability of depending for their separation on 

 characters commonly employed leads to the conclusion that 

 of some 'foo species hitherto described, only about half can 

 be maintained. The genus is held to be of American origin 

 since all Its groups that are known in the Old World have 

 more or less numerous representatives in America, while on 

 the other hand there are a number of well marked sections 

 of the genus in the New World which are not represented 

 in Europe and Asia. Furthermore, the different groups In 

 the Old World are quite sharply separated, while In America 

 intermediate forms are frequent; and whereas in Europe 

 the genus is sharply distinguished from all other Cruclferae, 

 this does not hold true in America. The important fact is 

 brought out that certain variable species widely separated 

 geographically, as for example Draha mageUanica and D. 

 hirta, the latter occuring In high northern latitudes, may 

 present forms growing in ecologically equivalent regions 

 which at first appear identical, but which as a matter of fact 

 belong to different sections of the genus, and are not even 

 closely related. 



Hildebrand reports that In the botanical garden of 

 Freiburg seedlings of Liiinui perenne from seeds obtained 

 at Stockholm produced In the first year the characteristic erect 

 fruits of that species; but plants raised from their seeds pro- 

 duced hanging fruits agreeing perfectly with those of Linum 

 aiistriaciim and suggesting a possible change from the former 

 into the latter species. 



C. E. Moss has compared the distribution of various 

 conifers and dicotyledons, and Inclines to the view that the 

 needle leaf and deciduous habit are ''due to enx'Ironmental fac- 

 tors, and may in themselves explain the frequent dominance 

 and successful competition of northern conifers among phyto- 

 genetically higher forms." 



