24 Proceedings of the Royrd Irish Academy. 



value in iudicatiiig \vl\ethei' an occidental plane is a young seedling or a small 

 tree; but is useless for the determination of the comparative ages of trees 

 over 20 feet high. 



2. A series of leaves from trees of P. orkntalis growing in this country 

 showed areas of vein -islets as follows : — 



Average area of the vein- 

 P. orientalis. islets of the leaf. 



Tree from Kashmir, said to be 19 years old, from seed, 0-05 sq. mm. 



Tree from seed of plane at Ephesus, 44 years old, . O'Oo „ 



Tree at Weston Park, probably 2o0 yeai-s old, . . OOG 



Tree at Kew, about KJO years old, .... 0'07 „ 



Tree from seed of plane at Thermopylae. 114 years old, 010 „ 



Tree fi-om seed of Bujiikdere plane, 50 years old, . 020 „ 



Cutting raised from last tree, 15 years planted, . 014 „ 



These measurements are too discordant to yield any satisfactory results. 

 The age of the trees of this species cannot be determined liy the size of the 

 vein-islets. 



3. The leaves of various trees of P. aeerifoUa gave the following measure- 

 ments of the veiu-islet-s : — 



Average nrea iif the vein- 

 P. acerifoliH. islets of the leaf. 



Tree at Ely, planted 250 yeara 012 sq. nun. 



Tree at Ranelagli, same age and size 012,, 



Tree at reamoip, probably of the same age, . . .011 „ 



Tree at Kew, planted 150 yeare 0-12 „ 



Tree at Kew, planted 120 yeai-8 012 



Tree at St. (Tenrge-in-tlie-East, I>ondon, planted 90 yenr.s, 012 „ 



Cutting from the latter tree, planted 12 years, . . 013 „ 



IJooted cutting from Slocock's nui-seiT, planted 1 year, 0-12 „ 



The aiea of the vein-islet« in the leaves of these different individual trees 

 is practically constant. This is some presumptive proof, if lienedict's views 

 are accepted, that all London Planes are of the same age, being ultimately 

 cuttings from one original tree. The large size of the vein-islets, correspond- 

 ing to that of P. ocridciitalui, about three years old, shows the extraordinary 

 vigour of /'. acfri/olia, if its great age, 250 years, is taken into account; and 

 confirms to that extent the view that it is a hybrid of the first generation. 



