Chermes abietis Choi.

Picea abies (L) Karst.
Picea mariana (Mill) B.S.P.

A polythalamous gall produced by the swelling of the base of the young shoots. Since the twigs are not usually killed the galls are sur- mounted by a variable length of normal stem. The galls in general vary from conoidal to nearly spherical in shape, but in some cases, owing to the stimulation not having aftected the entire circumference of the stem, the gall does not extend completely around it and is consequently less regular in outline. The surface of the gall is covered with the en- larged bases of the aborted needles. These give a faceted appearance to the gall and produce a likeness to a miniature pineapple.

Dimensions: — Longer diameter 2-3 cm.; shorter diameter 1-2 cm.

The gall in this case is a joint production of the cortex of the stem and the bases of the leaves of the host. The cells of the epidermis, lining the gall cavities, in some cases have been prolonged to form very short trichome-like structures. The hairs at the aperture of exit, as seen in Fig. II, are composed of one or two cells. The resin ducts that occur in the normal cortex are found consider- ably enlarged in the gall. In addition to these, there are out near the gall periphery numerous smaller resin ducts, as shown near the margin of Fig. II, that do not have corresponding structures in the unstimulated tissues. These additional ducts pass in from the swollen bases of the aborted leaves. A cross section near the base of these leaves cuts from four to six resin ducts, while a normal leaf does not contain more than two of these structures.

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

Reference: https://www.biodiversitylibrary.org/item/99818#page/21/mode/1up