One other very common and troublesome little fungus (Eurotium herbariorum) will for the present close our examples. This is found creeping over dried plants preserved in herbaria, on decaying fruit, preserves, and various other substances, sometimes animal as well as vegetable, but chiefly the latter. To the naked eye it appears as a myriad of little yellow spherical bodies, of the size of very small pins’ heads, resting upon fine cobweb-like threads (fig. 260). When magnified, the surface of the conceptacles is seen to be reticulated (fig. 261). In the interior the sporidia are borne, contained also, as in the former instance, in asci. It has been considered probable, but as yet not fully proved, that this mildew is a compound fruited (ascigerous) condition of an equally common mould (Aspergillus).
Dr. Shortt, of Chingleput, in a recent report on the growth and production of Indian Cotton, remarks that the plants are subject to the attacks of a kind of mildew. He writes:—“They appear in the form of rounded fibres or thallus, shooting up in the air, having the lamina of the leaf as a base, and feeling villous to the touch. The small fibrillæ that form the nap appear shooting up as sharp projections when seen by the naked eye; under the microscope they are found to consist of pointed tubes, interspersed here and there with minute granular cells. It first attacks either the upper surface of the petioles, or the margins of the leaf, gradually extending over the lamina, and matting together the whole leaf into a greyish-white, felty mass. At first it attacks the young shoots and tender leaves, preventing them from expanding. The extension of the parasite deprives the plant of its juices, and eventually either destroys or renders it sterile. The spores seem to be derived from the atmosphere, and finding the plant in a state fit to receive them, from either the results of excessive cultivation, or from the effects of heat and want of moisture rendering it unhealthy, and thus favouring the reception of the spores of the fungi. Another variety speckles the leaves with whitish dots. These remain separate, but the lamina is covered with them, and in time the leaf changes colour, becomes yellowish, and eventually dies away. This is evidently the disease called Bunt, or some variety of it, as it is seated beneath the epidermis, and eventually the spores escape. Under the microscope they seem to consist of small dark cells or spots attached to a thread-like mycelium.”
The writer seems certainly to have made a mistake in its affinities, and on the faith of the above quotation we should be more disposed to regard it as an Erysiphe. It is to be hoped that specimens of the affected leaves will be forwarded to this country for examination.
CHAPTER XIII.
SUGGESTIONS.
IF, in offering a few practical suggestions, we either repeat ourselves, or communicate common-place hints, those who may know already all we shall essay to tell them will please to pardon and pass on.
All the information essential under this head relates to collecting, examining, and preserving microscopic fungi.
Collecting does not differ, except in the objects themselves, from any other botanical collecting. Those who attempt it must be prepared to sacrifice their kid gloves and patent-leather boots, to put on waterproofs and perseverance, and come home sometimes disappointed. The requisites for good work are but few, and easily supplied. A strong knife, a pocket lens, and a box or leather bag, will be all that is really essential. But where shall we go—and when? Hedge-banks, the sides of ditches, borders of woods, anywhere, if the plants are to be found on which the fungi are parasitic. We flatter ourselves on being rather successful in collecting, and our favourite localities have always been the dampest places in woods, railway-banks, and waste places. It is a great mistake to endeavour to go over a large tract of ground. We have spent a whole day in a little chalkpit, which had fallen into disuse, and grown wild. Fifty yards into a wood is as much, as we attempt, when alone; and a spot six yards square has afforded us occupation for hours. It is better to examine a small space thoroughly than to scamper on, mile after mile, and find nothing.
When? is as much to be noted as where! All the year round we shall be sure of finding something of interest. As soon as the last patch of winter’s snow has melted from the ground, and green leaves begin to unfold themselves, the search may begin. Cluster-cups (Æcidium) will be the earliest forms encountered. On the leaves of Lapsana communis, and the pilewort, these will be found before the majority of plants have burst their buds. Henceforth, other forms will gradually appear, until May or June. One or two species of Puccinia will be seen in April or May, but from that period until autumn, species of Trichobasis will be common. In June and July the smuts belonging to the genus Ustilago are most plentiful, and from August to October Puccinia and its allied genera will have the ascendant; so that from March to October there is continually succeeding each other some species of parasitic fungus belonging to the Uredines. From October to March need be no more a season of repose from the search of these minute plants than from March to October. So long as the ground is not covered with snow there will always be something to find on dead leaves, rotten sticks, &c., when there is not a green leaf to be seen. But these belong to a section to which we have studiously avoided all reference in the foregoing pages.
General instructions will not always apply; but in most instances, the lowest and earliest leaves, in which vitality appears to decline, will be most likely to suffer from the attacks of fungi. This rule must not be too stringently applied; the species of Æcidium, for instance, will generally be found on vigorous green leaves.