Henky and Flood — The Ilislory of the London I'lane. 15 



absence of pubescence, in the shape of the enlarged head which surmounts the 

 elongated body, and in the persistence or fall of the style. In P. orientalis 

 the fruit-ball is very bristly on the surface, as the style persists. In P. occi- 

 denialis the fruit-ball is comparatively smooth, as the style at an early period 

 breaks off close to its insertion on the summit of the achene. In P. acerifolia 

 and some of its descendants, the influence of the American parent is shown in 

 the irregular breaking off at a late period of many of the styles either close 

 to or at a little distance from their insertion ; but as some of the styles persist, 

 the ball remains more or less bristly on the surface. 



The achene in all the species is surrounded at its base by a ring of rigid 

 unbranched hairs. The body of the achene is bare of hairs in P. occidentalis, 

 but covered with medium-sized matted branched hairs in P. orientalis, and 

 also in P acerifolia ; but in P. hispanica these hairs are very sparse. At the 

 junction of the body with the head of the achene a band of minute matted 

 branched hairs exists in all the species. The shape of the head of the achene 

 is specific ; cap-like, flattened, and bare of hairs in P. occidentalis ; conical and 

 covered with minute branched hairs in P. orientalis. The influence of the 

 American parent is shown in the glabrous head of the achene of P. acerifolia 

 and some of its descendants. The achene is perfect, containing an embryo, 

 in the two species and in most of the hybrids ; but in P. cantahrigensis and 

 P. dvjitata the embryo is not developed. 



These numerous minute differences in the achenes, fruit-balls, and leaves 

 of the various planes are exactly of the same kind and range as occur in 

 hybrids artificially produced, and afiford strong presumptive evidence that 

 from P. acerifolia, an accidental cross between two wild species, the other 

 planes, such as P.pyramidalis, P. hispanica, &c., only known in the cultivated 

 state, are descended. 



When the seed of a first cross is sown the seedlings produced constitute 

 a mixed and varied crop, in which are variously combined the characters of 

 the two parents. The best proof then of the hybrid nature of P. acerifolia is 

 the fact that it does not come true from seed, which appears to have been 

 known' to Lorberg in 1875. Two sowings made in recent years establish this 

 very clearly. There are now eight seedlings planted in the Queen's Cottage 

 grounds at Kew which were raised from seed of P. acerifolia that was sown in 

 April, 1911. These range in height from 4 to 10 feet, and are very diverse 

 in foliage, some closely resembling P. orientalis and others resembling P. 

 occidentalis, a few being intermediate. One of them appears to be identical 



' Gadeceau (1894) quotes a, note of Jules Biuneau, the celebrated horticulturist, that 

 on sowing P. acerifolia (commonly known to French nurserymen as P. occidentalis) there 

 is obtained a mixture of planes, the leaves of which are of diverse shapes. 



