Tetraneura ulmi. 



These galls grow on the upper surface only of the leaves 

 of the elm. As soon as the leaves unfold in the spring, the 

 apterous viviparous females begin their attacks. They are 

 the foundresses of the colonies. In consequence of the irrita- 

 tion they thus produce on the tissues of the leaf, there arises 

 around them exudation of sap, which, upon exposure to the 

 air, hardens, and is gradually increased in height until finally 

 the queen aphis is not only surrounded but completely enclosed. 

 The gall-structure has by then risen to a considerable height 

 above the plane of the leaf. Not only is the mid-rib thus 

 attacked, but the blade of the leaf is equally affected. The 

 structure thus formed is always pedunculated, although some 

 examples do not readily show it. Some have two peduncles ; 

 others have two cavities growing from one base. The structure 

 is closed in on all sides, there being merely a small opening at 

 the apex. The walls of the cell thus formed are thick, and the 

 queen within procures all her nourishment by sucking the sap 

 through her rostrum. Ecdysis occurs, usually about four times, 

 and then she commences to reproduce her young, to the number 

 of thirty to forty, which in time issue forth as alate females, 

 beginning during June and continuing intermittently through 

 the summer. Some trees are heavily loaded with thousands of 

 these galls ; their size also is considerably affected by the vigour 

 of the growth of the trees. 



In the extreme lower right-hand corner of the illustration 

 on opposite page a portion of a leaf may be seen in which the 

 basal part of the mid-rib is swollen, forming a bursiform growth 

 and bending the leaf at right angles. This is caused by 

 Tetraneura alba. It is figured by Kerner, vol. ii., p. 533. 



The illustration is of specimens gathered at Midhurst, Kent, 

 by Mr. R. R. Hutchinson. 



