What, then, we must ask ourselves, is the nature of these particles of dust? On September 27th, 1872, we picked from a vine, in the neighbourhood of Arbois, a bunch of grapes, of the variety called _le noirin_. The bunch selected, without any injury to a single grape, was brought to our laboratory in a sheet of paper that had been previously scorched in the flame of a spirit lamp, and the grapes were cut off with a pair of fine scissors, which had also been passed through the flame. By means of a badger-hair brush, thoroughly purified in water, each grape to which a portion of its peduncle remained attached, was washed in a little pure water. The successive washing of a dozen grapes in 3 c.c. of water was sufficient to make the water turbid; we then examined it under the microscope. Each field contained many little organized bodies, accidentally associated, now and again, with some very scarce crystalline spicules. As a rule, the organisms consisted of simple, transparent, colourless cells; some, indeed, of larger size had a yellowish brown colour, and were detached or united in irregular masses; and, lastly, there were club-shaped or bottle-shaped vessels, full of spores ready to germinate. We repeated this experiment with bunches of other varieties of grape, and also submitted to examination water in which the outer surfaces of gooseberries, plums, and pears had been washed; the result was in each case the same, that is, we found a great number of the same colourless cells, and the same irregular masses of darker cells, which latter, however, we must not confound with the masses of dead cells sometimes found covering parts of the epidermis of certain fruits. As we had purposely left each fruit attached to part of its peduncle, we wished to ascertain if these corpuscles proceeded from the grapes or from the wood of the peduncle. For this purpose we washed separately the surface of the grapes and the woody part of the bunch. The water in which the latter was washed was visibly more charged with the minute organisms than that in which the grapes was washed, although the latter was by no means free from them. Plate VIII. represents these corpuscles as they exist on the surface of fruits, magnified 500 times. The groups, _b_, _b_, _b_, ..., _c_, _c_, ... are of a brown colour, more or less dark, or of a reddish yellow; the cells _a_, _a_, ... are transparent. Amongst them are some spores of ordinary fungoid growths, and several cells which are probably the issue of a germination that had commenced in certain groups which have a hard, yellowish appearance, and which are provided with what seems to be a double case—_b_, _b_, _b_, ..., _c_, _c_, ..., a result of the moisture of the woody part of the bunch, or of rain that fell just before the commencement of our observations.