62 MASSACHUSETTS HORTICULTURAL SOCIETY. 



being not yet concluded. After three weeks the larva creeps 

 forth, and finds the nutritious gall material all ready prepared for 

 its food." 



A saw-fly larva may be recognized by its large head, and many 

 legs (twenty in all, six true and fourteen false) ; in some species 

 the larvae go underground to transform, and others pupate withia 

 the gall. 



The saw-fly galls which I hare found here, are willow eggs, on 

 the twigs of willow trees, and willow peas, willow apples, and 

 willow beans on the leaves. These latter occur in considerable 

 numbers, all through the season, on the leaves of large willow 

 trees, at Manchester, Mass., and I have also found them at 

 Jamaica Plain. 



But Dr. Adler found that in the family Cj^nipidae, which he calls 

 "gall-wasps," and we, usually, "gall-flies proper," the gall is 

 produced in quite a diflTerent way ; his observations showed him 

 that the mere puncture of the plant by the gall-fly, and act of 

 laying the egg gave no occasion for gall formation, and that it 

 was not until the tiny larva had crept out of the egg shell, and 

 wounded with its delicate jaws the soft plaut tissue surrounding it, 

 that a rapid cell-growth began, — so rapid that while the tail end 

 of the larva was still in the egg shell, in front of his head a wall- 

 like growth of cells arose. 



For the formation of the gall, it is essential that the larva, in 

 hatching, should find itself in a layer of fresh young cells, capable 

 of rapid growth and multiplication. Should the mother in any 

 way fail of placing her egg in exactly the right position, the larva 

 must die. 



If the egg is laid in a leaf, the gall formation begins in the 

 layer of cells in the under side of the leaf, as the upper surface 

 consists of firm cells which cannot further change. But if the egg 

 is laid in a bud, and the larva in hatching finds one of the unde- 

 veloped leaves, this as yet consists of similar cells, which, whether 

 they correspond with the upper or the under surface of the leaf 

 are all capable of development in a similar way, and the gall may 

 appear on both surfaces of the leaf, or cause a deformation of the 

 whole leaf. 



But how, from similar cells, galls so different from each other 

 in shape, size, and external appearance can be produced, is a 

 point not understood. The hairs which cover many galls are a 



