156 
SILVA OF NORTH AMERICA. 
SALICACEZ. 
borers in the living trunks and branches. It is also subject to numerous fungal diseases,’ although in 
North America the trees of this genus are more injured by insects than by fungi, of which only a species 
of Fusicladium appears capable, so far as is now known, of seriously affecting them. 
Many of the species of Populus are planted as ornamental trees and for screens and wind breaks, 
the rapidity of their growth and the ease with which they can be propagated by cuttings making them 
valuable for such purposes.” 
Populus, the classical name of the Poplar, of obscure derivation, was adopted by Tournefort’® and 
other pre-Linnzan authors for this genus. 
Poplars seriously ; and Cossus Centerensis, Lintner, has done much 
harm to Populus tremuloides and Populus balsamifera, as their larve 
live in the trunks of these trees. Other species of this genus or of 
allied genera have also been found on Poplars in different parts of 
the country. 
Among foliage destroyers one of the most serious pests is a leaf- 
beetle, Lina scripta, Fabricius, which in several of the western and 
southwestern states has been destructive to Poplar-trees by annu- 
ally defoliating them and thus finally causing their death. Lina 
Tremule, Fabricius, is also sometimes common. Chrysomela pallida, 
Say, Crepidodera Helxines, Linneus, and other beetles or their 
larve likewise feed on the foliage. Various species of Saw-fly 
larve feed on the Poplars and are liable to injure them. Among 
Lepidoptera, the larve of Acronycta Populi, Riley, frequently strip 
Poplars of their leaves, and other species of Acronycta are common 
on them. Of other Noctuide the genera Apatela and Catocala are 
represented on Populus by numerous species, but are rarely abun- 
dant enough to be noticeable. Species of Orgyia or Tussock Cater- 
pillars are sometimes troublesome ; and Clisiocampas and Hy- 
phantria sometimes defoliate these trees in the southwestern states 
and territories. 
The leaves are often mined by the minute larve of Lithocolletis 
populiella, Chambers, Phyllocnistis populiella, Chambers, and other 
Tineide, and the larve of other species sometimes roll or twist 
the leaves or their edges. 
Aphids are frequent on these trees, and galls formed by different 
species of the genus Pemphigus are often abundant, sometimes oc- 
curring as peculiar wrinklings or twistings of the leaves or as more 
or less spherical or hemispherical formations on the leaf-blades or 
leaf-stalks. 
1 The most serious fungal disease of Populus in the United States 
is probably due to the attacks of a fungus originally described by 
Libert as Oidium radiosum, and recently redescribed by Frank as 
Fusicladium Tremule. It is related to the fungi which cause the 
breaking and cracking of pears and apples, and is common on 
Populus tremuloides, having been observed twenty years ago on a 
tree in the Arnold Arboretum ; it is said to occur also on Populus 
balsamifera in the northeastern states. The disease manifests itself 
by the blackening in early summer of the young branchlets and 
leaves, which have the appearance of being killed by frost. No 
remedy for it has proved effectual, although it is evidently for the 
advantage of the tree to remove the blackened branchlets as soon 
as they are seen. 
A very curious and beautiful fungus, Taphrina rhizophora, Jo- 
hanson, attacks the young ovaries of Populus tremuloides and Populus 
grandidentata in the early spring, and has also been reported on 
Populus nigra Italica and Populus Fremontii in the United States. 
The ovaries affected by it are much enlarged and turn a golden 
yellow, so that the ament seen from a distance resembles a flower- 
ing raceme of Laburnum. 
The leaves of Populus are attacked in North America by a num- 
ber of species of fungi. Uncinula Salicis, Winter, the common 
mildew on the leaves of Willows, is likewise known on those of 
several species of Populus, which are also frequently attacked by 
Rusts belonging to the genus Melampsora, whose uredo condition 
appears as yellow spots on the leaves in summer and their teleuto- 
sporic condition as dark spots on the fallen leaves of winter and 
early spring. Another leaf fungus, Gleosporium Populi, Desma- 
ziéres & Montagne, is occasionally found on Populus alba and 
other species in the United States. 
The trunks and branches of Poplars are infested by a number of 
Ascomycetous fungi, Valsa nivea, Fries, being especially common 
on branches of Populus tremuloides, which are often covered by the 
white mouths of the perithecia. Namaspora chrysosperma, Per- 
soon, abounds on Populus tremuloides and Populus nigra Italica, 
appearing as small particles from which protrude minute yellow 
tendrils. Hypoxylon pruinatum, Cooke, covers large patches of the 
trunks of Populus tremuloides with its flat ashy gray tubercles. Of 
Hymenomycetous fungi peculiar to Populus in this country, Corti- 
cium pezizoideum, Schrenk, frequently covers the branches of Popu- 
lus tremuloides and Populus grandidentata with circular cushions of 
a deep red color. 
2 Wesmael, Bull. Féd. Soc. Hort. Belg. 1861, 335 (Monogr. 
Pop.). — Bailey, Bull. Cornell University Agric. Exper. Stat. No. 
68 (The Cultivated Poplars). 
3 Inst. 592, t. 365. 
