1885.] Found on the Black Walnut. 137 
bent from back to front also. In addition to these changes, when 
several galls are found on the same petiole (Fig. 3) this is often 
so much twisted as to bring them on the upper side of the leaf. 
The galls are elliptical in shape, the longer axis varying in 
length from 3™ to 15™™ and the shorter from 1™™ to 8™™ From 
above they appear slightly convex ; their centers are hairy and 
purplish-red in color and set in a green ring which is continued 
below into the petiole. Their average height is about 1o™™ In 
appearance they are not “unlike buttons which have their tops 
mounted in metal holders. 
The under surface of the gall is similar in general outline to 
its upper, as it abruptly contracts before passing into the petiole 
(Fig. 4), sometimes nearly clasping it either in the direction of 
its long or short axis. When several galls grow on the same 
petiole they may either run together or be entirely separate. If 
they coalesce great changes in size and shape are produced. 
The normal petiole is usually horizontal, but sometimes twists 
the leaf half way round (herbarium specimens). The cross sec- 
tion of the petiole near its base is of a reniform shape on account 
of a crease in its upper surface. The crease disappears further 
from the base of the petiole, which then appears elliptical in 
cross section. . 
The fibro-vascular bundles of the normal petiole of the walnut 
are such as are ordinarily found in the stems of dicotyledonous 
plants. The bundle is better developed as the apex of the petiole 
is approached. Even here, however, the bast is more abundant 
than the corresponding wood. An examination of that part of 
the petiole where the crease has disappeared shows a second row 
of well developed fibro-vascular bundles. Almost no trace of 
this can be seen in the lower part of the petiole (Fig. 5). 
Under a low power of the microscope a longitudinal radial 
section of that part of the gall near the pith of the petiole resem- 
bles a drawing of a geological section of the earth in which the 
strata are very much bent and folded (Fig. 10). The cells them- 
selves are bent, but the folding takes place mainly between con- 
tiguous cells. In comparing cross and longitudinal-radial sections 
of the gall (Figs. 9 and 10) the bast is found to be quite as abun- 
dant as in the normal petiole, but is spread over a wider area- 
The wood, too, is as scanty as before. The tracheary vessels 
have almost entirely disappeared. Tracheids have not only 
