The old story of “Eyes and no Eyes” is too often literally true, not only with the children it was written to amuse and instruct, but also with children of a larger growth who scorn such baby tales, and disdain such baby morals. Out of more than a thousand indigenous species of microscopic fungi, of which there is generally some evidence afforded of their presence visible to the naked eye, how few are there of the millions that inhabit our island who can count twenty species that they have ever seen; still fewer that have noticed one hundred. Amongst the twenty species known to the few will probably be included one which appears in autumn in prominent black spots, the size of a large pin’s head, or half a turnip seed, with the flat face downwards, sprinkling the under surface of blackberry leaves (fig. 39); with larger, reddish, purplish, or reddish-brown spots on the upper to indicate the presence of the fungus beneath. Just at the time when blackberries are ripe, these spots are in perfection on the leaves, and their eyes must have been sadly at fault who could ever have gathered their own blackberries without seeing the discoloured leaves. The coloured spots on the face of the leaf are due to the diseased state of the tissues caused by the parasite on the opposite surface. As much of the leaf as contains two or three of the black pustules should be removed carefully with a knife or sharp scissors, and submitted to microscopical examination; each will be seen to consist of a dense tuft of blackish, elongated, stalked bodies, clustered as in fig. 44, but much more numerously and closely packed together. These are the spores of the blackberry brand (Aregma bulbosum, Fr.). A few of these spores should be removed on the point of a sharp penknife, placed on a glass slide with a drop of distilled water or alcohol, covered with thin glass, and then viewed with a quarter-inch objective. Each spore has a stalk longer than itself, thickened below, and containing a yellow granular core. The spore itself is much longer than in any of the Pucciniæ, of a dark brown colour, and apparently divided by several transverse partitions into three, four, or more cells, the whole surface being covered with minute warts or prominences ([Plate III.] fig. 41).
In 1857, Mr. F. Currey investigated the structure of these spores, and the results of these experiments were detailed in the “Quarterly Journal of Microscopical Science.” One conclusion arrived at was, that “the idea of the fruit consisting of sporidia united together and forming a chain, is certainly not in accordance with the true structure. The sporidia are not united to one another in any way, but, although closely packed for want of space, they are in fact free in the interior of what may be called a sporangium or ascus.” To arrive at this conclusion, careful examination was necessary, and new modes of manipulation essential. The details of one method employed were to the following effect:—A sufficient number of spores were removed on the point of a lancet, and placed on a slide in a drop of alcohol. Before the spirit was quite evaporated, two or three drops of strong nitric acid were added, and the whole covered with thin glass. The slide was then warmed over a spirit-lamp, the acid not being allowed to boil, but only gradually heated to boiling point. By this means the fruit was found to consist of an outer membrane, nearly transparent, and studded with tubercles; that this membrane enclosed a number of cells which constituted the apparent joints, and which were naturally flattened at either end by mutual pressure. When the outer membrane was dissolved or ruptured, these cells escaped, and became detached from each other. The cells, thus set free, exhibited a brownish or yellow ring around a paler area, in the interior of which an inner cell was visible, sometimes globular, often irregular in shape. The examination of the ring was not entirely satisfactory; it appeared to be sometimes marked with concentric lines having the appearance of wrinkles. The inner cell had granular contents and a central nucleus. When perfectly free they were spherical in form, with a distinct membrane of their own; and colourless, except when acted upon by reagents. The means employed to determine the existence of these cells was to soak the spores in muriatic acid; then, upon pressure of the glass cover, the outer membrane and ringed cells were ruptured, and the inner cell escaped ([Plate III.] fig. 46).
Germination may be induced in these spores by keeping them in a moist atmosphere (fig. 45); but the mode does not differ from that described above as occurring in the “corn mildew.” Mr. Currey writes:—“I know no microscopical object of greater beauty than a number of fruits of Phragmidium in active germination.” By Phragmidium he means the Aregma of this work, of which Phragmidium is a synonyme.
Well may the reader remark on arriving thus far, “Does all this examination and detail refer to the fruit borne in the little blackish spots on bramble leaves, which I have hitherto overlooked?” Ay, and to several similar spots on other plants. Examine carefully the raspberry leaves in your garden, and you will probably find similar, but smaller, pustules also on the under surface ([Plate III.] fig. 42). We say probably, because none of our British species seem to be equally uncommon with this. During the past year we examined hundreds of plants, and did not find a single pustule. This species was named by Dr. Greville Aregma gracilis, which name it still continues to bear (fig. 43). Such a fate will not await you if you should proceed in the autumn to some chalky district where the burnet is common. Go, for instance, to Greenhithe or Northfleet, on the North Kent Railway, in August or September, where the burnet is plentiful, and the leaves will present the appearance of having been peppered beneath, from the number of minute pustules of the burnet brand scattered over the under surface (fig. 30, upper leaflets). Or if you prefer collecting nearer home, visit some neighbouring garden, if your own does not contain many roses, and the leaves will be found equally prolific in an allied species (fig. 36). Should gardens and roses be alike unattainable, any bank or wood will furnish the barren strawberry (Potentilla fragariastrum), and during the latter part of the summer, or in autumn, another species of Aregma will not be uncommon on the under surface of the leaves (fig. 33). All these species will be found accompanied by the orange spores of species of Lecythea, which some mycologists consider to be distinct fungi, and others to be merely forms or conditions of Aregma. These spores are represented in [Plate III.] figs. 31, 34, 37, and 40. From the magnified figures of the spores of the different species of Aregma (figs. 32, 35, 38, 41, and 43), it will be apparent that they have all certain features in common, i.e., cylindrical spores containing from three to seven cells. This may be called the generic character, common to all the species of the genus Aregma. Again, each species will be observed to possess its own distinct features, which may be termed its specific character. In one, the apex of the spores will be obtuse, in another acutely pointed, in another bluntly pointed, &c. In one species the number of cells will usually be four, in another five or six, in another seven or eight. The stem in one species will be slender and equal, in another thickened or bulbous. So that in all there will be some permanent peculiarity for each not shared by the others.
One other form of brand (Xenodochus carbonarius), presenting, it is believed by some, generic differences from all that we have as yet noticed, remains to be briefly alluded to. This form appears to be very uncommon in this country, but, when found, is parasitic on the leaves of the great burnet (Sanguisorba officinalis), a plant of local distribution. The parasite appears to the naked eye in small tufts or pustules resembling those of an Aregma, but, when microscopically examined, the cells of the spores are found to be numerous, indeed, considerably more than in the most complex Aregma (fig. 29). This, however, seems to be the only distinction, for the cells are free in the interior of the investing membrane, and in all points of structure, in so far as it has been examined, identical with Aregma. Whether it is logical to consider a four-celled spore an Aregma, and a seven-celled spore an Aregma, and exclude a ten or twelve-celled spore from the same genus on account of the number of its cells, does not appear to us clearly answerable in the affirmative.
During the course of this and the preceding chapter we have passed rapidly through four genera of parasitic fungi so nearly allied, that one is almost led to doubt the validity of the generic distinctions. These may be presented briefly thus:—
| Spores two-celled | Puccinia. |
| Spores three-celled | Triphragmium. |
| Spores four to seven-celled | Aregma. |
| Spores many-celled | Xenodochus. |
It has been seen that the habit, mode of growth, germination, and structure, except in the number of cells, scarcely differ; but it is not our province here to enter upon the discussion of such a subject.
The association of one-celled, orange-coloured spores with the brown two or more celled spores passed in review is another feature worthy of a passing notice, and which opens a field for discussion. It is generally admitted that these two forms are the production of the self-same mycelium or vegetative system, but it is not so generally admitted that they are but two forms or phases of the fruit of the same plant. It is not at all uncommon in the history of mycology to find two forms which were for a long time considered to be distinct plants producing different forms of fruit, and which bore different names, and were located in different genera, at length proved to be only the self-same plant in different conditions, and ending in one name being expunged from the list. Such a fate probably awaits, at no distant date, the orange spores which precede or accompany the species in the present genera. Already Tulasne and some others accord them no place in their system.
It may be added, for the benefit of any who wish to pursue the study of this interesting branch of Cryptogamic Botany, that the leaves of the plants containing the parasitic fungi now noticed may be collected and preserved by drying between folds of blotting-paper, or the leaves of a book, and will retain their character, with the exception of colour in the orange forms, so as to be eligible for examination at any period of the year for twenty years to come. Each species, when dry, may be transferred to an old envelope, and labelled outside with the name, date of collection, and locality; and one hundred such envelopes will constitute a miniature herbarium in a very small compass.