1782 The Trees of Great Britain and Ireland 



the tomentum on the branchlets and leaves, the latter having a different shape. It 

 is adapted to the humid and mild climate of western Europe; while P. alba, with 

 its dense protective covering against evaporation of water, is a native of drier and 



more continental regions. 



In the grey poplar, as in the white poplar, the leaves are fundamentally of two 

 kinds, different in shape, margin, tomentum, and petiole; but conveniently dis- 

 tinguished as "white leaves" and "green leaves." Some shoots bear only white 

 leaves, some only green leaves ; whilst others have green leaves towards the base 

 and white leaves towards the tip. The green leaves may be greyish beneath or 

 nearly devoid of tomentum. The size of the white leaves is inconstant, and 

 depends on the vigour of the branchlets. In old trees the green leaves are 

 preponderant, especially on the lower branches ; and such trees are popularly known 

 as P. canescens. In younger trees, and on the upper branches of older trees, the 

 white leaves are conspicuous ; and such trees are often erroneously called P. alba. 

 In addition to this variation, occurring on the same tree in its different stages 

 of growth, there are differences in the foliage of different trees, which require 



further study. 



A peculiar form, in which the leaves are thinner in texture, orbicular and not 

 deltoid in outline, and nearly glabrous beneath, is considered by Dr. C. E. Moss to 

 be possibly the hybrid P. canescens x P. tremula. Two pistillate trees^ with this 

 foliage, one at Hitchin, and another growing beside a stream between Caverham 

 and Icklingham, Suffolk, have pink stigmas, the colour of which suggests the influence 

 of P. tremula. These two trees flower a fortnight earlier than ordinary P. canescens. 

 Staminate trees with similar foliage have been found both in England and Ireland. 

 Mr. R. A. Phillips, who sends specimens^ from Lorrha, Tipperary, points out 

 that the catkins are shorter than in the typical grey poplar, about i^ in. long, 

 with fewer (4 to 7) stamens, and narrower scales. There is also a difference in 

 habit, the round-leaved trees have thick stiff ascending branches and short erect 

 twigs ; while the ordinary form has spreading branches and pendulous twigs. 



In P. tremula^ the foliage is all of one kind, similar in form to the green leaves of 

 P. canescens, but devoid of any trace of tomentum. The theory that typical P. canescens 

 is a hybrid * between P. alba and P. tremula rests on this apparent similarity of 

 foliage, and is not supported by evidence from the floral organs. Female trees of 

 the grey poplar are, however, rare, and the pistillate flowers have only been examined 

 in a few cases. So far as I can judge, P. canescens is a good species, being the 



' The pistillate tree with pink stigmas is P. canescens, Dode, in Mini. Soc. Hist. Nat. Autun. xviii. 26 (1908) (not Smith). 



2 Mr. Phillips recently sent me another form with leaves intermediate in shape and with flowers having eight 

 stamens. 



3 The suckers of P. tremula bear leaves which, in their shape and in the presence of a slight tomentum, simulate the 

 white leaves of P. canescens. 



* The older continental botanists, as Reichenbach, Icon. Fl. Germ. xi. 30, t. 617 (1849), and Hartig, NcUurgesch. Forst. 

 Culturpfl. 434 (1851), considered P. canescens. Smith, to be identical with the pubescent form of the aspen, P. tremula, var. 

 villosa. This has silky hairs on the leaves and branchlets, very different firom the tomentum of P. canescens. The occurrence 

 of true hybrids between P. tremula and P. alba is possible on the Continent. Radde, Pfiangenverb. Kaukas. 153 (1899), saw 

 a group of trees near Sotschi on the eastern shore of the Black Sea, which he considered to be of this origin, as the trees 

 strongly resembled P. tremula. Rechinger, in Verh. Zool. Bot. Ges. Wien, xlix. 284 (1899), discusses the hybrids in Austria. 

 Adamovic, Veg. Balkanldnd. 145 (1909), reports similar hybrids in eastern Roumelia. Cf. also P. albo-tremula, Krause, in 

 Jahrb. Schles. Ges. 1848, p. 130. 



