No. 615] SHORTER ARTICLES AND DISCUSSION 



1915. Appes 

 Her, H. J. 



Evidence as to the role which hybridization plays in evolu- 

 tionary change may be obtained from various insular floras by 

 a comparative study of the history of those plant types in 

 them which are prevailingly self-fertilized and those which are 

 prevailingly cross-fertilized, both as to the rapidity with which 

 new local species are produced and as to the frequency with 

 which old species disappear. With these points in view, analy- 

 ses have been made of the vascular plants in the floras of eight 

 islands or island groups: Ceylon, Mauritius, Socotra, New Zea- 

 land. Hawaii. Galapagos. Juan Fernandez and St. Helena. 1 In 

 all these there is a conspicuous, often predominant, element 

 in the flora which is strictly local or endemic, indicating that 

 each island has been the theater of considerable evolutionary 



Information is necessarily lacking as to the method of fertili- 

 zation of most of the species, but our general knowledge of the 

 reproduction of the higher plants allows us to divide them into 

 three main types. The dicotyledons and petaliferous monocoty- 

 ledons, possessing floral organs which in the great majority of 

 cases are attractive to insects, are doubtless prevailingly cross- 

 pollinated. In the glumaceous monocotyledons, on the other 

 hand (chiefly Graminea\ Cyperacea? and Juncacea?), the floral 

 organs are not so constructed as to favor cross-pollination, and 

 it will probably be agreed that crossing is much less common 



* These analyses are based on the following authorities: Trimen, Hand- 

 book of the Flora of Ceylon; Baker, Flora of Mauritius and the Seychel- 



