ACTING STATE ENTOMOLOGIST. 
43 
causes the singular pod-like growths, about one-eighth inch long, upon the Uppei sui- 
face of the leaf of the wild plum-tree (Primus americana)* which often swarm so 
prodigiously, that I calculate that the number of young Mites, in one small clump of 
Plum-trees, frequently exceeds the number of human beings now living and breathing 
upon the face of this earth. This will perhaps be considered a wild exaggeration ; but 
see what the figures themselves will say. I have often counted as many as sixty of 
these galls on a single leaf, and each gall contains towards the end of July seveial scoies 
of microscopically minute young Mites. Such a leaf will therefore contain about 
3,000 young Mites, and putting the human population of the whole globe even at the 
enormous number of 900,000,000, it will only take 300,000 such leaves to veiify mj 
estimate. Now, Dr. Fitch has calculated (New York Reports I. p. 127) that there are 
about 17,000 leaves on a young cherry-tree only ten feet high ; and I presume that there 
would be fully as many on a plum-tree of the same size. Let us suppose that in a 
particular group of such plum-trees there are, on the average, only 3,000 leaves on each 
tree fully stocked with young Mites, as calculated above ; or, if any leaves are less 
fully stocked, as many leaves in all as would be equivalent to 3,000 fully-stocked leaves. 
Then it follows that there need only be 100 plum-trees, each about ten feet high, in 
the group, to make up the whole number of 300,000 fully-stocked leaves, which, ac¬ 
cording to the calculation, are required in order to sustain a population of young Mites, 
equal to the very highest estimate that has ever been published of the entire human 
population of this earth! 
Now pluck one of the gall-bearing leaves from such a group of 100 plum-trees, which 
might easily grow upon a piece of ground much smaller than a common-sized village- 
lot. Open one of the galls on it. Examine its inhabitants with a powerful magnifiei. 
You will see at once, that all this infinite multitude of infinitesimally minute beings 
are as perfect in every limb, and in every joint of every limb, and probably in every 
nerve and muscle of their tiny bodies, as the gigantic animal that is watching their 
operations through a piece of glass. They are all busy. They are all evidently healthy, 
and happy, and in the full enjoyment of their existence. They contribute, in no wise 
to our pleasures or to our necessities ; neither do they molest or trouble us in any way 
whatever. We are separated from them by as wide a gulf, as if they were denizens of the 
far-away planet Neptune. And yet we fondly dream, in our vain glorious hallucination, 
that all this vast world of life and happiness—so minute in size, but so inconceivably 
large in numbers —was created for our sole benefit, and has no right to exist but by 
our sovereign permission and at our good will and pleasui e ! 
*For the benefit of the scientific reader, I copy from my Journal the description of this one gall. 
The general reader will be thankful that I omit the descriptions of the other nineteen galls : 
Gall Pruni crumena, new species. On Prunus americana. A fleshy, smooth, elongate, blunt-tipped, 
fusiform, opaque, hollow gall, constricted at its base, and with a few erect hairs, 0.10-0.16 inch long, 
and about four or five times as long as its extreme breadth. Walls of the gall thin. Color outside 
a very pale green, often tinged with rosy; inside, rough and of a rosy color. Always grows upon the 
upper surface of the leaf, whole trees frequently swarming with it, the number of galls on a single 
leaf varying from one to sixty. Ten galls opened July 27th all contained Acarus larvae, scores of 
them in each gall. These larvm are exceedingly minute, of a hyaline-whitish color, of the usual elongate - 
oval form, thrice as long as wide, six-legged, with their legs arranged as usual. They are very sluggish- 
Some of a yellow color were crawling on the leaves outside the galls. A similar but distinct gall 
CCerasi crumena, Walsh MS.) is almost equally abundant on the leaf of the Wild Black Cherry (Cerasus 
( serotina .) 
