CHAPTER XXX. BUNT OF WHEAT. Tilletia Caries, Tul. THE disease of wheat generally known as bunt is recognised in some districts as pepper - brand, smut balls, bladder-brand, stinking-smut, stinking-rust, and even smut. Its ravages are almost confined to cultivated wheat; it rarely occurs on barley. A distinct species occurs on wheat in the United States. The scientific name of the fungus which causes bunt in wheat is Tilletia Caries, Tul. Tilletia is named after Matthieu Tillet, who wrote the Dissertation sur la cause qui corrompt et qui noiriet les grains de blèd dans les épis, Bordeaux, 1755, and a similar work published in Paris in 1755. Caries means rottenness or decay. The meaning of the popular name, bunt, is very obscure. We have the word bunter, which means an offensive person (woman), and the verb bunt, to swell; the former may be a cognate derivative. Dr. Murray of Mill Hill informs us that the word bunt is used, for a fungus in the same way as touchwood, by writers of the seventeenth century. This is perhaps the most likely origin. The cavity or belly of a sail is called the bunt, and the material of the sail bunting. The bellying part of a seine-net is also called the bunt, which name may have been transferred to the blight in reference to its fishy smell. Bunt may be a corruption of burnt. In the fields it is difficult without experience to distinguish bunted from sound wheat; there is very little indeed to indicate the presence of the hidden foe; this is why the disease is so dreaded by farmers. As in many other fungoid ailments the fungus appears to excite an abnormal growth of chlorophyll, and the spikes of affected plants are commonly greener than the sound ones. Even on examining the ears it sometimes happens that but little seems amiss; it is not until the glumes and pales are pushed aside that the dark diseased seeds become visible. Sometimes the bunted grains burst whilst still in the ear, and the escaped spores stain the glumes and pales a dark colour. Practised eyes readily detect these slight black stains. A bunted grain of wheat is illustrated at Fig. 114, A, FIG. 114.-BUNT OF WHEAT. Grains of wheat destroyed by Tilletia Caries, Tul. with a transverse section at B, and a longitudinal section at C, enlarged five diameters. Reference may be made to Fig. 42 for a normal grain of wheat, and to Fig. 45 for an example of ear-cockle, all engraved to the same scale. The external appearance of bunted grains of wheat is different from healthy grains. Bunted wheat seeds are shorter and wider than healthy ones; they are dwarfed in height and distended in width, and generally somewhat pointed towards the base. Instead of being pale buff in colour, they are of a somewhat dark, dull green tint. They are frequently cracked, as shown at A, and from these cracks a black powder emerges. On cutting affected seeds in two, the outer coat of the grain is found to be weak and brittle, and its whole inner substance a mass of black powder, which has replaced the natural inner farinaceous material of the grain. On crushing bunted wheat between the fingers the black pulpy powder feels soft and greasy, and a foetid odour resembling decaying fish is dispelled; hence the popular name, stinking-rust. One of its old botanical names is Uredo foetida, Baeur. Bunted grains do not occur as isolated examples in the ear; the rule is that every grain in an affected ear is bunted. When these bunted grains are ground into flour their Spores of the Bunt fungus, Tilletia Caries, Tul. presence is made known to the miller, not only by the black streaks they cause in the white flour, but also by the disgusting odour which arises at the time of crushing. The black powder, when placed under the microscope and magnified 400 diameters, is seen as at Fig. 115, one mass of beautiful brownish spores, with a few fine mycelial threads, to which some of the spores will be seen still attached; the supporting threads are best seen in young examples, for as the fungus approaches maturity, the threads break up into dust and perish. The spores are spherical, or sometimes slightly oval, reticulated and slightly spinulose, reminding a microscopist of pollengrains belonging to the Campanulacea, the colour of course being different. They are so small that a single If these spores are kept in moist air or on a wet surface for three or four days, they will germinate, as at Fig. 116, A, enlarged 1000 diameters. The epispore bursts, and a thick septate tube is protruded. This tube, after it has grown to three or four times the diameter of the spore, forms a sort of small terminal crown, and on the minute papillæ of this crown it bears four, eight, or ten rodlike sporidia, as shown at B. When these sporidia are fully grown, and whilst still adherent to the apex of the germtube, they coalesce, as at CC, by means of short transverse tubes. When these conjugated bodies drop from the supporting tube they germinate and produce secondary sporidia of a different form, as shown at DD. At times the supporting threads of these conidia are extremely long and jointed throughout; at other times there is no supporting thread, but the conidium may grow from the end of a secondary spore. Sometimes the sporidia are produced whilst the secondary spores are still attached to their supporting stem. A spore or conidium so growing is illustrated at G. The conidia, in turn, are capable of germination and the production of conidia of the third order, as at EE. Sometimes they so germinate without the spores, DD, falling from their attachment. the secondary and tertiary sporidia, as at D and E, germinate, they produce a septate thread of extreme tenuity, as at F, and on this thread the bunt spores are at length borne, as illustrated in Fig. 115. Sometimes bunt spores do not produce, on germination, the minute crownlike terminal cell, with its conjugating secondary spores; but the thick germ-tube grows for a great length, branching and rebranching, and all the time forming septa. The vital material is chiefly confined to the terminal end of each branch. When this mode of growth takes place, conjugating spores are never formed. When In some instances the secondary spores become conjoined in two places instead of one, as illustrated by Mr. Berkeley, and confirmed in two instances by Dr. Oscar |