Aphid Gall (Unclassified),

Host Populus balsamifera L.

A pouch-like gall on the under surface of the leaf, produced by a fold in the blade near the base of the midrib. One edge of the fold is attached along this midrib. The slit-like opening, which is on the upper surface of the leaf, extends the full length of the gall. This species resembles very closely the gall produced by Cecidomyia majalis Bass. The general structure is shown in Fig. 7.

Dimensions: — Length along line of attachment to midrib, 10-12 mm. ; Width, 4-5 mm.

In the part of the leaf blade that forms the gall all resemblance to the normal mesophyll has disappeared. A compact mass of tissue has taken its place, the cells of which are much larger than normal mesophyll cells. Towards the interior of the gall the cells become smaller and richer in protoplasmic contents. The upper epidermis forming the interior of the gall remains practically normal, except that it produces longer and more abundant trichomes than when unstimulated. These trichomes are usually three cells in length. A cross section of this gall shows two small groups of cells with porous laminated sclerenchymatous walls, one of which is situated near the midrib and the other exactly op- posite on the other side of the gall opening. Thus each side of the gall aperture is bordered by a band of sclerified cells, as shown in the trans- verse section of Fig. 8.

- A Cosens: (1912) A contribution to the morphology and biology of insect galls ^©

Reference: https://www.biodiversitylibrary.org/item/99818#page/17/mode/1up