IRISH GARDENING 



VOLUME XIII 

 No. .'46 



Editor J. W. Besant 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



APRIL 

 191S 



The Black Poplars. 



By Phofi:ss()1i A. Henry, i\I.A., Royal (JoUr^c of Science, Dublin. 



Till': Blark Poplars are distinguislifd from the 

 othrr kinds by their leaves having the same 

 tint of green above and below, so that it is im- 

 possible to tell the upper from the lower sm'face 

 \)\ the colour alone. The name is not due to 

 any blackness in the wood, bark, &c., of these 

 trees, and is evidently applied in contradistinc- 

 tion to the white and grey poplars, whose leaves 

 ha\t' a woolly under surface, and to the balsam 

 poplars, the lower siu-face of the leaves of 

 \\ liieh have a peculiar whitish tint, not caused 

 li\- the presence of wool or down. In the 

 as[)ens, another class of ]K)plars, the leaves 

 have a paler tint of green beneath than above. 



Each region of the Northern Hemisphere out- 

 side the tropics has its peculiar species of 

 lihi'k, white, balsam, and aspen poplars. The 

 main species of black poplar are Populus nigra 

 in Europe, and Populus deltoidea in Eastern 

 North America. We need not now concern^ 

 (iiii'selves with the species of Western North 

 America, Populus Fremontii, W^islizeni, and 

 mexicana, which are practically \mknown in 

 this coimtry, except by one or two specimens 

 of the first-named, in botanic gardens. 



The American black poplar, P. deltoidea, 

 called Cottonwood in the United States, is 

 I'eadily (listing\iishal)le by the presence of a 

 fringe of cilia around the i'(lges of the leaves, 

 readily seen with a lens, and by two or more 

 c()nspicuous glands at the l)ase of the blade, 

 close to its junction with the stalk. Th^ 

 stigmas are three or foui', and the stamens 

 .")() or 60 in the flowers of the .\jnerican species. 

 In the European P. nigra, there are no marginal 

 cilia or basal glands on the leaves, and the 

 stigmas are only two, and the stamens 15 to 30. 

 These differences are easily remembered, as 



there is a deficiency in the Europi'an species 

 in the characteristics noted. 



So much foi' the distinctions which hold good 

 for the two main species; but the subject is 

 complicated by the sub-division of each into 

 several forms. There are two geographical 

 forms of P. nigra, each occujiving a distinct 

 territory in the wild state. The typical foi'ui, 

 so called because it was the one that Linnaeus 

 knew best, and jilanted in his garden at Upsala, 

 is prevalent in eastern Europe, where it forms 

 immense groves on the alluvial flats of the big 

 rivers like the Daniibe, Save, Dnieper, Po, &c., 

 growing in ground too wet for ash, oak, and 

 elm. It is distinguished by the complete* 

 absence of hairs on its twigs and leaves. The 

 other form of the European black poplar, P. 

 nigra betulifolia, is confined to France and 

 England, and differs from the last in having 

 hairy twigs and leaves. It may be pojiularly 

 styled " English Pdack Poplar." 



Practically speaking, a black ])oplar, having 

 the trunk covered when old with burrs, anil 

 with wide-spreading, closely-set branches and 

 hairy twigs and leaves, may be assigned to 

 var. betulifolia. It is not indigenous in Iic- 

 land, where it is, however, occasionally planted. 

 It bears wind better, but grows much slower 

 than the 'hybrid black poplars, of which I will 

 speak presently. Old trees attain a great age, 

 one at Mallow being perhaps the finest in Ire- 

 land. In 1000, it measm-ed 00 feet in length, 

 and 10.'; feet in girth around the trunk at 5 feet 

 above t1ie ground. There is one nearly as large, 

 but with a hollow trunk, at New Eoss; and 

 others at Callan, from which I have raised 

 seedlings that grow very slowly. 



To the public^ at large, the Lombardy po])lar 



