Populus l 77 1 



The poplars are typical light-demanding trees, incapable of bearing shade, their 

 branchlets and leaves dying when not exposed to full light. This is well seen 

 when two Lombardy poplars are planted close together, the shade of the taller of the 

 two killing the branches on the adjacent side of the other. In connection with this 

 demand for light, which necessitates sparse branches and foliage, the poplars normally 

 shed many of their smaller branchlets in autumn. The process 1 by which this is 

 effected is similar to that by which the leaves are cast off, a zone of corky tissue 

 being formed at the point where the rupture subsequently takes place, the branchlet 

 leaving when it falls a circular scar on the main branch to which it was attached. 



The genus Populus comprises about twenty-five species, inhabiting the extra- 

 tropical regions of the northern hemisphere from the Arctic Circle southwards ; in 

 North America extending to Lower California and northern Mexico ; throughout 

 Europe and northern Africa; and in Asia, extending as far south as Asia Minor, 

 Syria, Mesopotamia, Persia, Afghanistan, the Himalayas, China, and Japan. 

 Towards the extreme north certain species often form great forests ; elsewhere 

 poplars are most common in alluvial land bordering rivers, streams, and swamps ; 

 but occasionally they form a part of the deciduous forests. 



The genus is divided into five sections ; and the following key, based mainly on 

 the characters of the leaves and buds, includes all the species in cultivation, with the 

 more important hybrids ; and in addition, three species, mainly of botanical interest, 

 which we have not seen in England in the living state. 



I. Turanga, Bunge, Beit. Kennt. FL Russ. 498 (1848). 



This section differs from the others in the remarkable polymorphic leaves, 

 and in the deeply cleft disc of the flowers, which does not remain persistent at 

 the base of the fruit. 

 1 . Populus euphratica, Olivier. 2 



Northern and eastern Africa, Syria, Mesopotamia, Persia, Turkestan, 

 Afghanistan, north-west India, Mongolia, north China. 



A tree 50 ft. high. Leaves coriaceous, greyish green, of the same colour on 

 both surfaces ; on young trees, linear or oblong, entire, short-stalked, and willow- 

 like ; on old trees extremely diverse, ovate, oblong, rhombic, or orbicular, lobed 

 or cut, long-stalked. 



Not hardy in Great Britain. 3 This poplar, and not a willow, 4 is the 'arabim 

 of the Psalms, cxxxvii. 2, the trees growing by the rivers of Babylon, on which 

 the Jews in captivity hanged their harps. 5 



1 This natural fall of branchlets, effected by a vital process, was termed dadoptosis by Berkeley, in Gard. Chron. 

 1855, p. 596. It has been observed in oaks and willows, as well as in poplars, and Shattock gave a complete account of it 

 in the case of the aspen mjourn. Bot. xxi. 306 (1883). This phenomenon appears to have been first noticed by J. Main, 

 Hcrrt. Register, iv. 193, fig. A (1835), where a fallen branch of the black poplar is figured. 



2 Voy. Emp. Othom. figs. 45, 46 (1807). This is a very variable species, which has been variously treated by botanists. 

 Gombocz, in Math. Termes. Kbzl. xxx. 71, 72 (1911), recognises several varieties, and treats P. pruinosa, Schrenk, as a 

 distinct species. P. illicitana, Dode, in Bull. Soc. Demi. France, 1908, p. 163, lately found near Elche in Spain, appears to 

 be only naturalized there, and is identical with the ordinary form of the species in Morocco and Algeria. 



3 Spath, Catalogue, No. 91, p. 51 (1893-1894), states that a plant sent to Lauche from Turkestan in 1881 soon died. 

 It was reintroduced by General Korolkow, who sent it to Spath in 1892. 



* Salix babylonica, Linnaeus, was so called, because it was erroneously supposed to be the tree of the Psalms. Cf. p. 1752. 

 6 Cf. Koch, Dcndrologie, ii. pt. i. p. 507 (1872), and Ascherson, in Sitzi. Ges. Nat. Fr. Berlin, 1872, p. 92. 



