Externally the “bunted” grain is plumper, and whilst the corn is still green these will be of a brighter green than the rest (Plate V. fig. 84). When broken, the farinaceous interior will be found replaced by a minute black dust of a very fœtid, unpleasant odour, and greasy to the touch (fig. 85). This powder constitutes the spores of the “bunt” mixed with myceloid threads. It may happen that much of the corn in a field is “bunted,” and the discovery not made till the wheat is being ground for flour; then the odour and colour will speedily decide the produce to be unfit for human food. We have not the least doubt that “bunted” corn, when ground with flour, is injurious in proportion to its extent, whilst at the same time we can scarcely conceive an intelligent miller grinding up a sample containing any large proportion of “bunted” grains in ignorance of the fact.
If we break open a grain of wheat infested with the “stinking rust” or “bunt,” and then place some of the powder in a drop of water on a glass slide, and submit this to the microscope, first using the half-inch power, then the quarter, or fifth, and finally an eighth or tenth, we shall find that this minute dust consists of myriads of globose brown bodies termed spores, which possess certain reproductive functions. These spores will be found mixed with a number of delicate branched threads, to which they are attached by a short stalk or pedicel, visible with the higher powers (fig. 86). The surface of the spores you will also observe to be beautifully reticulated. These features just described as visible in the “bunt” are the characteristics of the genus to which it belongs (_Tilletea_), and of which it is the only British species. An allied species infests the Sorghum or durra, a grain but little cultivated in Europe, but found extensively in Africa and Asia, and also apparently found on the _Bajra_ of India.
The interesting experiments of the Rev. M. J. Berkeley on the germination of “bunt” spores have been already alluded to. They were undertaken shortly after the outbreak of the potato disease, to ascertain, if possible, the mode by which the minute spores of fungi inoculate growing plants; and although at that time only a bare suspicion of the nature of the bodies resulting from the germination of “bunt” spores was entertained, succeeding examinations in the same direction have brought to light extraordinary facts, and manifested the progress of the successive developments of four generations. The spores of “bunt” are larger than those of the different species of “smut,” and reticulated on the surface (Plate V. fig. 86). When these are made to germinate a kind of stem is protruded (fig. 87), upon which small clusters of elongated thread-like spores of the second generation, or sporidia, are produced (fig. 88). After a time these spores conjugate, or become united by short transverse processes in the same manner as has been observed in some of the lower forms of Algæ (fig. 89). The conjugated spores in the next stage germinate and produce a third kind of fruit, different from either of the preceding, and constituting a third generation (fig. 90). These in turn germinate and produce a fourth order of reproductive organs (fig. 91), so that in the process of growth the “bunt” spores evidently pass through four generations. Hence, as one result, the number of germinating bodies is greatly increased, as well as their power of inflicting injury in a corresponding diminution in size. There are still many points in the history of the growth and development through successive generations of the “bunt” spores, but enough is known, on the one hand, to show that this is a true vegetative parasite, and not merely a diseased condition of the tissues of the wheat plant, and on the other that it is perfectly distinct from all the phases of the other and similar parasitic fungi which affect the wheat crop.