270 



THE AM ERIC AX A". I TV RATI ST [Vol. LII 



among them than in the petaliferous types. Finally, in the 

 vascular cryptogams, the very frequent occurrence of bisexual 

 gametophytes seems to insure a still greater prevalence of self- 

 fertilization. 



The vascular flora of each island was divided into these three 

 groups which were studied comparatively. Determination was 

 first made as to the percentage of local or endemic species in each 

 group. This degree of endemism provides us with a rough meas- 

 ure of the extent to which new forms have been developed on the 

 i>land, and thus allows us to compare the rapidity of evolution 

 in one floral group with that in the others.- In the following 

 table are set forth the percentage of endemic species in each of 

 the three main groups which we have mentioned, and for each 

 of the islands : 



TABLE I 



prevailingly crossed than among those which are prevailingly 

 selfed, being highest among dicotyledons, lower among gluma- 

 ceous monocotyledons and lowest among vascular cryptogams. 

 The same fact appears among genera, for 95 per cent, of the 

 endemic genera of these islands belong to petaliferous types and 

 only 5 per cent, to the glumaceous monocotyledons and vascular 

 cryptogams. These facts all point to the importance of hybridi- 

 zation as a factor in the production of new species. 



The other aspect of evolutionary change, namely the disap- 

 i Of course not all the endemic forms can be regarded as of local origin, 



spread. The proportion of these, however, which have not subsequently 

 undergone specific change, and thus developed true local types, is probably 

 small. 



