The beautiful purple stipitate cups of Bulgaria sarcoides, which may be seen flourishing in the autumn on old rotten wood, are often accompanied by club-shaped bodies of the same colour; or earlier in the season these clavate bodies may be found alone, and at one time bore the name of Tremella sarcoides. The upper part of these clubs disseminate a great abundance of straight and very slender spermatia. Earlier than this they are covered with globose conidia. The fully-matured Bulgaria develops on its hymenium clavate delicate asci, each enclosing eight elongated hyaline sporidia, so that we have three forms of fruit belonging to the same fungus, viz. conidia and spermatia in the Tremella stage, and sporidia contained in asci in the mature condition.[X] The same phenomena occur with Bulgaria purpurea, a larger species with different fruit, long confounded with Bulgaria sarcoides.
On the dead stems of nettles it is very common to meet with small orange tubercles, not much larger than a pin’s head, which yield at this stage a profusion of slender linear bodies, produced on delicate branched threads, and at one time bore the name of Dacrymyces Urticæ, but which are now acknowledged to be only a condition of a little tremelloid Peziza of the same size and colour, which might be mistaken for it, if not examined with the microscope, but in which there are distinct asci and sporidia. Both forms together are now regarded as the same fungus, under the name of Peziza fusarioides, B.
The other series of phenomena grouped together under the name of polymorphism relate to forms which are removed from each other, so that the mycelium is not identical, or, more usually, produced on different plants. The first instance of this kind to which we shall make reference is one of particular interest, as illustrative of the old popular creed, that berberry bushes near corn-fields produced mildewed corn. There is a village in Norfolk, not far from Great Yarmouth, called “Mildew Rollesby,” because of its unenviable notoriety in days past for mildewed corn, produced, it was said, by the berberry bushes, which were cut down, and then mildew disappeared from the corn-fields, so that Rollesby no longer merited its sobriquet. It has already been shown that the corn-mildew (Puccinia graminis) is dimorphous, having a one-celled fruit (Trichobasis), as well as a two-celled fruit (Puccinia). The fungus which attacks the berberry is a species of cluster-cup (Æcidium berberidis), in which little cup-like peridia, containing bright orange pseudospores, are produced in tufts or clusters on the green leaves, together with their spermogonia.
De Bary’s observations on this association of forms were published in 1865.[Y] In view of the popular belief, he determined to sow the spores of Puccinia graminis on the leaves of the berberry. For this purpose he selected the septate resting spores from Poa pratensis and Triticum repens. Having caused the spores to germinate in a moist atmosphere, he placed fragments of the leaves on which they had developed their secondary spores on young but full-grown berberry leaves, under the same atmospheric conditions. In from twenty-four to forty-eight hours a quantity of the germinating threads had bored through the walls and penetrated amongst the subjacent cells. This took place both on the upper and under surface of the leaves. Since, in former experiments, it appeared that the spores would penetrate only in those cases where the plant was adapted to develop the parasite, the connection between P. graminis and Æcid. berberidis seemed more than ever probable. In about ten days the spermogonia appeared. After a time the cut leaves began to decay, so that the fungus never got beyond the spermogonoid stage. Some three-year-old seedlings were then taken, and the germinating resting spores applied as before. The plants were kept under a bell-glass from twenty-four to forty-eight hours, and then exposed to the air like other plants. From the sixth to the tenth day, yellow spots appeared, with single spermogonia; from the ninth to the twelfth, spermogonia appeared in numbers on either surface; and, a few days later, on the under surface of the leaves, the cylindrical sporangia of the Æcidium made their appearance, exactly as in the normally developed parasite, except that they were longer, from being protected from external agents. The younger the leaves, the more rapid was the development of the parasite, and sometimes, in the younger leaves, the luxuriance was far greater than in free nature. Similar plants, to the number of two hundred, were observed in the nursery, and though some of them had Æcidium pustules, not one fresh pustule was produced; while two placed under similar circumstances, but without the application of any resting spores, remained all the summer free from Æcidium. It seems, then, indubitable so far that Æcidium berberidis does spring from the spores of Puccinia graminis.
It has, however, to be remarked that De Bary was not equally successful in producing the Puccinia from the spores of the Æcidium. In many cases the spores do not germinate when placed on glass, and they do not preserve their power of germinating very long. He reverts then to the evidence of experiments instituted by agriculturists. Bönninghausen remarked, in 1818, that wheat, rye, and barley which were sown in the neighbourhood of a berberry bush covered with Æcidium contracted rust immediately after the maturation of the spores of the Æcidia. The rust was most abundant where the wind carried the spores. The following year the same observations were repeated; the spores of the Æcidium were collected, and applied to some healthy plants of rye. After five or six days these plants were affected with rust, while the remainder of the crop was sound. In 1863 some winter rye was sown round a berberry bush, which in the following year was infested with Æcidium, which was mature in the middle of May, when the rye was completely covered with rust. Of the wild grasses near the bush, Triticum repens was most affected. The distant plants of rye were free from rust.
Fig. 107.—Cells and pseudospores of Æcidium berberidis.
The spores of the Æcidium would not germinate on berberry leaves; the berberry Æcidium could not therefore spring from the previous Æcidium. The uredospores of Puccinia graminis on germinating penetrate into the parenchym of the grass on which they are sown; but on berberry leaves, if the tips of the threads enter for a short distance into the stomates their growth at once ceases, and the leaves remain free from parasites.
