Hknry and Flood — The History of the, London Plane. 25 



4. Tlie leaves of the planes of the second generation show the following 

 measurements of the vein-islets : — 



Average area of Uie vein- 

 islets of the leaf. 



P. hispanica, . . . 0-10-0'13 sq. mm. 



r. pyramidalis, . . . 0-14-OlG 



P. ciineata, . . . 0-08-0-13 



P. digitata, . . . 0-14-0-16 



P. pai-viloba, . . . 0-14-0-17 



P. cantabrigensis, . . . 0"14 „ 



The oldest of these, judging from its liistory, is P. hispanica ; and it is 

 practically identical with F. accrifolia in the area of the vein-islets. The 

 other planes originated later, and except one [F. cuncata) show larger average 

 areas. This is what might be expected, if Benedict's view is correct. 



Synopsis of the species of Platanus. — A synopsis of the six living species, 

 showing the main differences in the character of the leaves and fruits, is now 

 given : — 



A. Adult leaves glabrous or nearly so, and as a rule conspicuously 

 toothed in margin. 



1. P. onentcdis, L. See p. 16. Greece, Cyprus, Crete, Ehodes, and Asia 

 Minor. 



Leaves with five elongated lobes. Fruit-balls, '2-Q on the peduncle, bristly, 

 the styles persisting. 



2. P. occidentalis, L. See p. 17. Eastern North America from Toronto to 

 Texas. 



Leaves with three or five short lobes. Fruit-balls solitary, smooth, the 

 styles falling off early. 



B. Adult leaves with dense tomentum persisting on the lower surface ; 

 usually entire in margin, rarely with minute teeth. 



* Zohes of the leaf, 5 or 7, elongated, extending beyond the middle of the blade. 



3. P. Wrightii, Watson. Arizona, Mexico. 



Leaves variable at the base, often deeply cordate ; sinuses between the 

 lobes narrow. Fruit-balls, 2-4 on the peduncle, comparatively smooth, the 

 styles breaking off near their insertion. Achene ^■ery tomentose, as in P. 

 oricntalis, but with the apex more rounded and flattened than in that species. 



K.I. A. PKOC, VOL. XXXV, SECT. B. [•/'] 



