26 Proceedings of the Royal Irish Academy. 



•4. P. racemosa, Xuttall. California. 



Leaves similar to those of P. Wrujhtii, but base less deeply cordate and 

 lobes broader. Fniit-balls, 3-7 on the peduncle, very bristly, the styles per- 

 sisting. Acheue glabrous except for the basal ring of long hairs and a trace 

 of tomentum at the junction of the elongated body with the shortly conical 

 head. 



** Lobes of the leaf, 3 or 5, short, not extending to the middle oftlu blade. 



5. P. .Vexieana, Moricand. Xorthern Mexico. 



Leaves, 3-5-lobed, densely white tomentose beneath. Fruit-balls solitaiy, 

 bristly, the styles persisting. Achene similar to that of P. orifntalis. 



6. P. Lindeninna, XIartens and Galeotti. Southern Mexico. 



Leaves with usually three very short lobes, ending in bristle-like points, 

 and covered beneath with a dense rusty tomentum. Fruit-balls, 2-5 on the 

 peduncle, bristly, the styles pereisting. Achene with tomentose conical style 

 aud short glabrous body. 



NoTE-s nv pROFE-sson A. Hexry. 



The numerous measurements of the lobing and vein-islets of the leaves, 

 and the drawings and descriptions of ihe fniits, have been earned out by 

 Miss Flood. For the rest of the paper I am mainly responsible. 



A full account of the genus Platanus, with details of the distrilmliun, 

 cultivation, remarkable trees, itc, of the variotis species, is given by Elwes and 

 Henry, " Trees of Great IJriuin," iii, C11-G29 (1908). In this work, p. 620, 

 I did not accept as correct the hybrid origin of Platanus acerifolki. The 

 researches on elms, poplars, and other cultivated trees which I subsefjuently 

 carried out, led me to reconsider this view, and to undertake the investigations 

 which are the subject of this paper. In my opinion the evidence establishes 

 beyond doubt that the London Plane is of hybrid origin. 



