AN ENCYCLOPEDIA OF HORTICULTURE. 



199 



POPULUS (the ancient Latin name = palpulus, akin 

 to palpitare, to tremble ; probably so called from its 

 trembling leaves). Poplar. OED. Salicinece. A well- 

 known genus of hardy, deciduous trees, with terete or 

 angular branchlets, and having scaly buds, covered with 

 resin ; eighteen species have been described, natives of 

 Europe, Central or mountainous and Northern Asia, and 

 North America, including Mexico. Catkins loose, appear- 

 ing before the leaves, the males often pendulous ; flowers 

 of both sexes usually shortly pedicellate, the females some 

 times on an elongated pedicel, racemiform. Leaves alter 

 nate, sometimes on laterally compressed, tremulous petioles 

 usually broad, penniveined, and trinerved at the base 

 entire, toothed or lobed ; stipules narrow, membranous 

 fugacious. Some of the Poplars are amongst the most 

 rapid growers of all hardy forest-trees. They thrive under 

 a variety of conditions as regards soil, &c., but do best in 

 damp situations, such as along watercourses, &c. All are 

 readily increased from cuttings, inserted in the open 

 ground ; soon after the leaves have fallen is the best 

 time to do this. The weeping forms are generally 

 grafted on tall, straight stems of the common upright- 

 growing ones. 



Fungi. Many kinds of Fungi live on dead branches 

 and stems of Poplars, and a good many also on living 

 parts ; but the only one of the latter that is usually very 

 noticeable in gardens is that known as Exoascus aureus 

 (Taphrina aurea). This Fungus produces very con- 

 spicuous spots on the leaves of Populus nigra. These 

 spots bulge on one surface, usually the upper, so as to 

 appear almost hemispherical, and may be from ^in. across 

 up to a much larger size, when two or more fuse together. 

 The spots are usually duller green above, bright golden- 

 yellow below; but sometimes the yellow colour is on 

 the upper surface. The microscope shows that the colour 

 is due to a layer of rather long cells, fixed to the surface 

 cells of the leaf by one end, but free in the rest of their 

 length. Each is full of a large number of small, round 

 cells or spores, which escape by bursting the wall of 

 the containing cell. When abundant, this Fungus is very 

 conspicuous from its colour, and is very hurtful to the 

 young trees, which it chiefly affects. 



The best remedy is the removal and destruction of the 

 leaves, or of the branches, and even the whole trees if 

 much infested, as soon as the Fungus appears. Perhaps 

 the application of solutions of potassium sulphide or 

 potassium permanganate might destroy the Fungus. 



Insect Pests. Poplars are liable to the ravages of a con- 

 siderable variety of insects, mostly beetles and moths. A 

 number of them are described elsewhere, and these species 

 are merely mentioned here, the reader being referred 

 to the fuller information given under the headings quoted. 

 The wood of the trunks is bored into by the Poplar 



FIG. 251. POPLAR HORNET CLEARWING MOTH (Sesia 

 apiformis). 



Hornet Clearwing Moth (Sesia apiformis, see Fig. 251). 

 the larvae of which live for about two years in the trees. 

 See Sesia. The larvae of the Goat Moth (which see) 

 are even more destructive. The young branches and 

 the twigs are bored into by the larvae of certain beetles 



Populus continued. 



of the genus Saperda. The insects are rather slender, 

 and nearly cylindrical, and of the general form shown in 

 Fig. 252. 8. carcharias is about tin. to Hin. long, 

 dusky-black, with grey or yellow pubescence, and rather 

 long antennae ringed with grey and black; the wing- 

 cases are narrowed towards the tips. 8. populnea is 

 about iin. long, black, slightly hairy, and marked with 

 pits over the surface; the thorax bears three yellowish 

 lines ; the wing-cases are not narrower behind ; they 

 are covered with a yellowish pile, and bear three or 

 four large, yellowish spots; the antennae are ringed with 

 ashy-grey and black. The larvte of this species live in 



Fio. 252. A, SAPERDA POPULNEA, natural size; B, BRANCH OP 

 POPLAR, showing ravages committed by it. 



gall-like swellings in the branches (see Fig. 252) of 

 Poplars and of Willows. There are a few other species 

 of Saperda, but they do not call for special mention. 

 Branches tenanted by the larvae (shown by their galled 

 or withered state) should be cut off ; this is usually suffi- 

 cient to kill the larvaa, but it is well to have the branches 

 burned. 



The leaves are devoured by several beetles of the 

 family ChrysomeliddB the leaf-eating beetles par excel- 

 lence. Lina Populi is frequently very abundant on 

 Poplars. This beetle is nearly $in. long, oval, and 

 shining blue-black; the wing-cases red, except a black 

 tip, and very finely pitted; feet, and tips of antennas, 

 black. The larvae are shaped much like those of Cocci- 

 nella (see Ladybird) ; the head, the hinder part of the 

 body, and the legs, are black; the rest of the body is 



