﻿170 FIELD AND FOREST. 



unknown butterfly which makes the embryo of Polygonum arviculare 

 assume a horn-like appearance, and thirteen (perhaps fifteen) Curcu- 

 lionidce. 



Group II. Closed larval galls properly so called. The limits of 

 this group are difficult to prescribe. The larval cavity is at first always 

 spherical and is never surrounded by sclerenchyma. The galls are 

 broadly attached but never included in tissues that do not enter into 

 the formation of the gall, and the larva usually abandon the galls, 

 having gnawed away the interior. 



This group includes about 10 Dipterous galls among which are 

 those of the Selaginella discovered by Braun and described by Stras- 

 burger, the well known malformation on the stems of Poa nemoralis 

 caused by Cecidomyia poae, Bosc, some on Tamarix, 6 or 8 Lepidop- 

 tera that cause galls on German plants in North Africa, and at least 

 twenty of the CurculiomdcB. 



Order II. Imago galls, a perfect insect of the section Hymenoptera 

 bores with its ovipositor some portion of the plant in which its eggs 

 are laid, and at the same time pours into the wound a peculiar fluid 

 that causes the formation of the gall, which is usually nearly or 

 fully grown before the egg hatches. 



Family I. Galls of the Tenthredonidce or leaf wasps. The wounds 

 in this case remain visible covered with a corky bark. They are made 

 by the insects saw over the middle of the vascular bundles and an egg 

 laid therein. The swelling does not take place precisely in the wound 

 but a little way off. The galls show on both sides of the leaf, but 

 usually unequally, and the larva; leave the gall to undergo transfor- 

 mation in the ground. Two stem galls on Clematis and Loniccra, 4 on 

 Salix and Populus, ten Leaf galls on Salix and Lycium. 



Family II Galls of the Cynipidce. In these the wound usually 

 closes entirely, but sometimes leaves a small brown canal leading to 

 the interior. This in my opinion is the result of moistening the cells 

 with formic acid which the gall wasps usually secrete, the acid kills 

 the cells which become brown. It must be observed however that 

 these brown canals are often (possibly always) caused by Inquilina 

 and parasites that lay their eggs in the tissues of the galls or in the 

 larva itself. 



The egg is shaped like a long stemmed pear with the neck at first 

 protruding out of the wound but this dries up, and the egg is shut in. 



