INSECTS INJURIOUS TO THE COTTON-WOOD. 



Ex-planation. — a, incipfent gall on the under side of the leaf; 6, coiresponding bulge on the upper 

 side : c, fully formed gall, showing the lips slightly separated, so as to permit the escape of the mature 

 insects ; d and e, incipient double galls, one being located on each side of the mid-rib ; /, the wingless 

 female ; g, the mature winged insect. 



POPLAR-LEAF GALL-LOU^. 



(Pemphigus populicaulis, Fitch.) 

 Order of HOMOPTERA. Family of Aphip^. 



The Cotton-wood fPopuhis moniUfera, AitoUy), thongli one of the least 

 valnable of our shade trees, is nevertheless worthy to retain its ])lace 

 among- our shade-trees on account of its rapid growth, and the ease and 

 certainty with which it can be propagated, thus often becoming avail- 

 able where other trees have failed. For these reasons there is a con- 

 siderable demand for it, in proof of which we may state that we have 

 recently seen a statement of twelve thousand of these trees having been 

 shipped, upon one order, to a Swedish colony in Nebraska. The health 

 and growth of the Cotton-wood, and some other species of the poplar 

 family, are sometimes seriously impaired by different kinds of excres- 

 cences on the twigs and leaves, constituting what are technically known 

 as galls, and formed by as many diffei-ent si)ecies of the gall-making- 

 aphides. One of these is a large corrugated gall, formed on the ends of 

 the twigs, often near the tops of the trees, turning black when mature, 

 and adhering to the tree through the winter, and making unsightly ex- 



