N.B.—Since the foregoing chapter was in type, the Rev. M. J. Berkeley informs us that both Mr. Broome and himself have examined the mould on dock-leaves, to which we have given the name of _Peronospora obliqua_, and have come to the conclusion that it is truly a member of that genus, and not hitherto described; but they are also of opinion that it is the same mould as one described by Dr. Montagne as _Ascomyces Rumicis_. We concur with them in thinking it deficient in the important characteristics of _Ascomyces_, and therefore retain its proposed name of _P. obliqua_. ------------------------------------------------------------------------ CHAPTER XII. _WHITE MILDEWS OR BLIGHTS._ NOTWITHSTANDING the inconvenience to ourselves of calling very different fungi by the same common name of “mildew,” the popular mind does not recognize the inconvenience, since it scarcely troubles itself to inquire whether they are not all the same thing. In obedience to this custom, we again write of “mildew,” or “blight,” as it is called in some districts, but of a very different kind to that which is so detrimental to growing crops of corn. In the present instance it is our intention to illustrate a group of fungi which are exceedingly common, and which differ greatly in appearance and structure from any to which we have had occasion to allude. To obtain a general knowledge of these forms let our reader proceed at once to a clump of rank grass; if it is his fortune to dwell in the country, the walk of a few yards will suffice. Let him examine this clump more carefully, perhaps, than he has been accustomed to do, and we venture to predict that he will find some of the leaves covered with what appears to be a dirty white mould, or mildew (Plate XI. fig. 235). One of these leaves should be collected as carefully and conveyed to the microscope as speedily as possible, taking care not to touch, or brush it against any other object so as to disturb the arrangement of the delicate little threads upon its surface. If a small portion, say about an inch, is cut from this leaf with a sharp pair of scissors, and laid upon a slide, or pinned down upon a strip of sheet cork, so as to keep it flat, and then submitted to examination under the microscope, with an inch power, a beautiful forest of crystalline vegetation will be observed. If the examiner on this occasion should not possess a binocular microscope we are sorry for him, because in that case he will not see all that is to be seen under the greatest advantages. If we ever truly enjoy looking through such an instrument, it is on an occasion like this, when a low power is all that is needed, and the object is required to be seen in relief. It is scarcely possible to convey an adequate idea of the beauty of such a scene as the microscope reveals upon this fragment of grass-leaf. Little bundles of delicate threads, clear and crystalline, are seated upon a slender