4S 



GEOGRAPHICAL DISTRIBUTION 



particular meridians 



other sources: 



of distribution, the evidence is in 



accordance with that derived from 



DIAGRAM 5. 



Distribution by phyllotaiis 



General ptTcentaee- 

 !..-h .•«• tltfi-uat 

 „ opposite 



. . . 



. . ■ 



• • • 



fiV3 

 357 



Alternate 



Abctic. 

 Opposite 



20°/ 



Alternate 



100°/ o 



America. 



Opposite 



Alternate 



■Pi 



Japa 



Opposite 



Alternate 



53*4°/o 



CAUCASU8. 



Opposite 



46-6° /o. 



Alternate 

 71"5°/o 



SlBEBIO-TUBKESTAN 



Opposite 



28-57« . 



Alternate 



Tibeto-Chx^a 

 Opposite 



O' 



5 1 <o« 





The most notable features of this diagram are 

 (1) the absence of opposite-leaved species 



along 



the American and European 



meridians. In America Proper there are no opposite-leaved species 

 Europe only one (P. verticillata) ; 



in 



along 



the 



(2) the progressive increase in the percentage of opposite-leaved species 



Siberian meridian of distribution; and 



(3) the practical equilibrium of the percentage from end to end of the Japan - 



Himalaya meridian. 



"While these facts strikingly confirm the evidence already advanced in support of the 

 hypothesis of meridional migration, they throw some light on the evolution of the character 



in question 



d 



on the history of the g 



The lower percenta 



of 



pposite-leaved 



species in the Circumpolar province appears to favour the hypothesis that the genus was at 



first characterised by alternate lea 



only 



It is 



ely possible otherwise to suppose 



that the original eiroumpolar flora was uniform, and to account for the absence of opposite- 

 leaved forms from the American meridian. On the other hand, the absence of such forms 



