for although the above facts were in themselves unanswered, yet the so-called scientific botanists urged that the fungus upon the barberry leaves belonged to a totally distinct genus (Æcidium) to that upon the wheat (Puccinia). There is evidence to show that many careful observers, even at this time, suspected that the Puccinia was connected in some way with the uredospores which occur as its precursors. This remained a suspicion only until Tulasne demonstrated that the connection between the uredospore and the teleutospore existed not only in the species in question, but was the general rule amongst the Uredineæ. In 1861, De Bary showed that many of the Uredineæ not only had uredospores and teleutospores, but also that the latter gave rise in many cases (but not in all) to æcidiospores, and conversely the acidiospores to uredospores. De Bary also pointed out that in certain cases the sowing of germinating teleutospores upon the same species. of host-plant which bore them was not followed by any result. Amongst these were Puccinia graminis. It further occurred to him that, as there were several æcidia unaccompanied on their host-plants by any other spore-form, these might belong to Uredines which passed a part of their life upon one plant and the remainder upon another. Familiar with the facts already known to the practical agriculturist concerning the barberry and wheat mildew, he put the matter to the test of actual experiment. In 1864, he sowed Puccinia graminis on barberry and produced the Æcidium, and in 1865 he did the converse culture, by sowing the acidiospores upon rye. The results obtained by his experiments with P. graminis led De Bary to investigate the life-histories of other æcidia, which, like Ec. berberidis, are unaccompanied by any other spore-form on the same host-plant. Thus he found that P. rubigo-vera has its acidiospores upon Lycopsis In the arvensis, and P. coronata upon Rhamnus frangula.1 following year, 1866, Oersted showed that Gymnosporangium sabine and juniperinum were similarly connected with Ræstelia cancellata and cornuta; and in 1867, that G. clavariaforme was connected with R. lacerata. In 1869, Fuckel indicated the connection of Uromyces junci with Ec. zonale. In 1873, Magnus worked out the life-history of P. caricis in its relationship to c. urtica; and Schröter, in the same year, the heterocism of Ec. rununculi bulbosi and Uromyces dactylidis. Since this time these facts have been repeatedly verified by numerous workers, and our knowledge of the subject has continuously increased, as the subjoined tabular statement will show. * Gymnosporangium clava-Roestelia lacerata riæforme Uromyces junci *Puccinia caricis * Uromyces dactylidis *Puccinia poarum Calyptospora goeppertiana Acidium ranunculi-bulbosi Peridermium pini Ecidium berberidis Ecidium asperfolii De Bary 1865 Ecidium rhamni De Bary 1865 Roestelia cancellata Magnus 1873 Schröter 1873 1874 Winter 1874 1 De Bary, "Neue Untersuch. über Uredineen," 2nd paper (1886), pp. 208-214. * is affixed to those species which I have personally investigated. † to those of which I have repeated the cultures, but am not able to confirm the above statements. The question naturally presents itself to us, Why are some species heterocious and others not? One reason is pretty obvious, namely, that those Puccinia and Uromyces which are heterocious occur upon host-plants whose cuticle is, if not silicous, at least very hard and difficult for the germtube of the promycelial spore to pierce-namely, on grasses, Carices and Junci. This, however, can hardly be the only reason, since Schröter has produced the Ecidium on Euphorbia cyparissias from Uromyces pisi; in this case both. the host-plants have soft epidermal cells. The Coleosporia and Melampsoræ afford similar instances. Whatever may have been the cause or causes in bygone ages, the fact is that at the present time so completely have these parasites become heterocismal in habit, that the most profuse application of their promycelial spores to the graminaceous host is always without result. CHAPTER VIII. MYCELIUM OF THE USTILAGINEÆ. THE vegetative mycelium of the Ustilaginea is to the parasite one of its most important organs, for by it, and by it alone, does the fungus derive its nutriment from the host-plant upon which it subsists. Yet the mycelium is of all parts that which is least frequently observed; nor can this be wondered at when one remembers that, like the mycelium of the Uredineæ, it can be seen only by careful search by cutting and teazing out numerous thin sections of the host-plant. We owe most of the information we possess upon the mycelium of the Ustilaginea to Fischer von Waldheim, although, among others, both Kühnt and Hoffmann had previously figured it. It exists most abundantly in the tissues of the host-plant, in the immediate vicinity of those places in which the spores are developed; but it can also be found in other parts of the affected plant-in the monocotyledons particularly in the stem, but especially in the nodes and in the root-stock. In the dicotyledons it is not so easily found at a distance from the spore-beds; still, in them too it has been seen in the root-stock and * Fischer von Waldheim, "Pringsheim Jahrbücher" (1869), vol. vii. Pp. I, 2. † Kühn, "Krankheiten der Kulturgewächse," 2 aufl. 1859. Hoffmann," Ueber der Flugbrand." 1866. stem, especially in the nodes. The mycelium consists of hyaline tubes, frequently septate, and enclosing watery or pellucid, frequently vacuolated contents (Plate V. Figs. 1, 2). Its walls vary in thickness, but very often they have a distinctly double contour. The number and frequency of the septa are subject to much variation; in some instances they are close together, at others they are only found at distant intervals. This is also the case with the mycelial ramifications; sometimes the hypha do not extend for more than 2μ without branching, at others they extend for 20μ or more without dividing. These long unbranched hyphæ are found mostly in the internodes; in the nodes themselves not only are the branches more abundant and convoluted, but here too are encountered, more abundantly than elsewhere, the little intercellular haustoria, or suckers, which characterize the mycelia of many of the Ustilagineæ. The mycelium ramifies not only between the cells of the host-plant, but, frequently piercing their walls, grows through them. Its diameter varies from 2 to 5μ. The addition of caustic potash to a section of the host-plant containing mycelium renders the latter more distinct, and otherwise clears up the preparation; so does prolonged treatment in glycerine. Its walls are not composed of cellulose, as they do not show any blue reaction when treated with sulphuric acid and iodine; but in some cases, as with U. maydis and Sorosporium saponaria, they do get an external coating of cellulose from the tissues of the hostplant, which, completely investing them, hides them from view (Plate VI. Fig. 3). The mycelium of almost all the Ustilagineæ permeates more or less the whole of the affected plant, and although in the advanced state we can find it only near the spore-beds, yet originally it could be found in all parts of the axis of the young plant. In this it differs from the localized mycelia of most of the |