1885.] Sound on the Black Walnut. 139 
These cells contain a purplish-red coloring matter which is solu- 
ble in water. If this is removed the cells are found to contain a 
large quantity of a brown granular substance. The hairs of the 
gall are so unlike normal hairs in shape, position, contents and 
origin that they can scarcely be looked upon as modified trich- 
omes. Ensconced among the hairs which are distributed over 
the surface of the gall are found the eggs of the mite which pro- 
duces it. 
In order to know the changes which the gall has undergone in 
reaching its mature state, it would be necessary to make a careful 
study of the specimens of the gall from its first appearance to its 
full development. I hope to do this in the future. Possibly it 
may not be too presumptuous to venture a few predictions 
founded on a comparison of the gall with the normal. petiole in 
regard to development: 
1. The gall must have started very early. The fact that the 
gall hairs cannot be looked upon as modified trichomes has been 
already referred to. Vestiges of the normal trichomes would be 
found among the gall hairs if the petiole had been far enough ad- 
vanced for them to appear, but no such remains are found. The 
epidermal cells of the gall are so thin-walled and so unlike the 
thick-walled and regular epidermal cells of the petiole in form, 
that they could have originated from them only at an early 
period. Comparison of the tissue beneath the epidermis in the 
gall and petiole does not suggest that one was derived from the 
other. 
2. The development was doubtless inward, the stimulant, no 
matter of what nature, acting on the outside. The position of 
the eggs, the mode of oviposition of mites and the fact that no 
sign of their having pierced the tissue can be found, suggests 
this. The bending and folding of the fibro-vascular tissue would 
seem to suggest that the stimulant caused a greater growth in 
length than in breadth, and this produced the lateral pressure 
which pushed up the tissue. 
3. The value of these various modifications to the mite may be 
seen in a general way. The hairs of the gall give the very best 
protection to the eggs, the parenchyma is an excellent cushion 
and is firmly supported by the tracheids which, with the other 
