WILLOW GALLS 109 
these. On May 29th, some branches of willow were 
brought to me, on the leaves of which were small tumors 
or welts of green color, that were beginning to redden. 
The welts were long and smooth like beans; they were 
not placed like the osier balls on the side of the leaf 
turned towards the ground, and therefore easily dis- 
placed, but arise on both sides of the leaf that envelops 
them, are situated near the large central vein or 
nerve, and are found to the number of two and some- 
times three on a leaf. I observed several and found 
that they contained a white caterpillar like the one found 
in the two species of osier, and I observed also, that 
many of these welts had been pierced, and in their cav- 
ities there only remained the excrement of the cater- 
pillar, which had already escaped; whereupon I became 
hopeful of seeing the transformation but in vain; for al- 
though I carefully kept my leaves enclosed in boxes, the 
caterpillars would never come out, and after a few days, 
I invariably found that they were dead. As you may 
possibly be curious to see how the plants look that bear 
the caterpillars, and of which generation the herbalists 
have not made mention, as far as I know; I send you 
drawings of them herewith, calling your attention to the 
fact, that the smaller drawing of the caterpillar is its 
natural size, and the larger, its appearance under a 
microscope of ordinary power. 
I do not know of any other caterpillars produced by 
trees, but Father Kircher repeatedly states, in the twelfth 
book of the " Subterranean World," that the mulberry 
tree produces the silkworm, on being impregnated with 
the seed of any chance animal, which penetrates the sub- 
stance and the juices of the tree. In order to ascertain 
the truth of this statement, I not only studied the trees 
