The pustules, when fully open, are from one-sixteenth to one-eighth of an inch in diameter, usually round, but sometimes slightly oval in form, and placed mainly in almost straight rows lengthways of the branch, as shown in Fig. 44. These pustules appear on wood of all ages, from two years upward, and in what may be termed patches, ranging from a few inches to a foot or more in length, and more frequently on the upper side than the underside of the branches. [Illustration: FIG. 44. HAZEL FUNGUS.] This fungus is undoubtedly indigenous, and its host plant is the common American hazel (_C. Americana_). From a very careful search, I have not been able to find any clump of these bushes of any considerable size that was entirely free from pustulous stems. But on these wild plants it seems to do but little harm, for if a stem is killed, another soon springs up from the roots to take its place; but when this fungus invades our orchards and gardens and attacks filbert trees, we recognize it as an implacable enemy. How far the spores of this fungus are likely to be carried by the wind, transported on the clothes of a person, or the hair of domestic animals, I do not know, but it certainly is not safe to plant the susceptible species and varieties within a mile of the wild hazel bushes, unless the planter is prepared to use fungicides freely on his trees. There are certain phases of this filbert blight that are rather obscure and scarcely explainable; as, for instance, its virulence among some species and varieties, and almost if not total absence among others. So far as my observation extends, I have never found it attacking the native beaked hazel (_Corylus rostrata_), and my correspondents in the Northwest and in the Pacific States assure me that no blight on the hazel has, as yet, been found there, and its absence is probably due to the fact that the common hazel (_C. Americana_) is not an inhabitant of these regions. In a neighbor's garden just across the highway from my own, there are, at this time, four old European hazelnut trees, fully twenty feet high and as many years old. They are of two varieties: one a small round nut, the other a long, slender nut, but neither of much value, because of their small size. The trees, however, are perfectly healthy, never having suffered from the blight, although these four are all that remain of a long row of choice European varieties all planted at the same time. Blight destroyed the better varieties, while these inferior ones continue to thrive and are exceedingly productive.