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en masse, are blackish, but frequently, however, with an olive-brown or yellowish lustre, especially when viewed in an oblique light. U. segetum, when it occurs in wheat, has a distinctly golden lustre, but when on Avena elatior it is sooty black. Physiological research will possibly show that these two forms are specifically distinct. With U. scabiosa the spores in bulk are flesh-coloured, and in U. succise they are quite white. Individually, the spores of the various species, as seen under the microscope, afford a considerable range of colour-black, dark violet, brown, olive-brown, and yellowish, or quite colourless. In some species a germ-pore is said to exist, through which the promycelium is protruded in germination; but these germpores of the Ustilaginea are by no means so marked a formation as in the Uredineæ. In U. tragopogi the germpore is said to occupy from one-quarter to one-half the epispore. Much more commonly do we find, as in T. tritici,† a small opening which splits into a rift as the promycelium grows out. In Thecaphora hyalina the germpore is round and paler in colour than the rest of the epispore; moreover, it is smooth, while the epispore is verrucose. Upon the whole, although germ-pores probably exist in all species, they are inconspicuous, and are very easily overlooked in the smaller spores. The reticulations on the epispore of Sphacelotheca are shown by the action. of sulphuric acid, when examined by a high magnifying power, to consist of a series of distinct palisades, placed vertically. As a general rule, the spores are globose, but in most species this is subject to a certain amount of variation; they often have one diameter rather longer than the other, but more frequently they show the result * De Bary, "Morph. und Physiol.," p. 128.

*

Brefeld, "Hefenpilze," p. 48.

F. von Waldheim, "Sur la structure des spores des Ustilaginées " (1867), pp. 243-245.

of mutual compression by being flattened in one or more directions. In U. caricis they are often flattened on one side, so as to be subhemispherical. In size they vary from 4μ in U. hypodytes to 30μ or more in Urocystis fischeri. They may be simple or collected into spore-balls (Sorosporium), in which case they appear, when seen separately, as in T. hyalina, to be segments of a sphere, being convex externally, but internally more or less wedge-shaped. In Urocystis the spore-balls are surrounded by a variable. number of barren spores or pseudospores, which are paler in colour, often almost hyaline; these do not germinate.

Hartsen found that the spores of the U. maydis would not yield their colouring matter to any of the ordinary solvents, but that strong sulphuric and nitric acids decolourized the epispore, rendering it more transparent without at once destroying it, so that the contour of the exterior remains unaffected. Although the spores sometimes burst, yet by these reagents the structure of the epispore can be conveniently examined. In nitric acid. the spores of the U. maydis swell up, and after a time they dissolve, giving off an odour of bitter almonds. Sulphuric acid is the better reagent to employ in the examination of the spores, as, although it decolourizes and renders the epispore transparent, yet it does not so rapidly destroy the latter.

Hartsen, "Compt. rendus " (1874), pp. 441, 442.

CHAPTER X.

GERMINATION OF THE TELEUTOSPORES OF THE

USTILAGINEÆ.

AT the beginning of the present century, Prevost* discovered the fact that the spores of U. segetum and T. tritici, when placed in water, would germinate. He observed the process in Tilletia to consist of the protrusion of a germ-tube and the development upon it of primary spores, which became united in pairs below, and which bore above the secondary spores. His observations were confirmed by De Candolle,t by Caron and Vandenhecke, and by Mr. Berkeley, and they have been accurately described and delineated by almost all the more recent observers. With U. segetum Prevost observed the germ-tube, and that it gave off small secondary branches. His observations were confirmed by Tulasne,|| Bonorden,¶ Kühn,** and others. Little additional light had been thrown upon the subject,

*

1807.

Prevost, B., "Mém. sur la cause immédiate de la Carie." Montauban :

+ De Candolle," Physiol. Veget." (1832), vol. iii. p. 1436. In 1835 referred to by Tulasne, "re Mémoire," p. 38.

§ Berkeley, "Propagation of Bunt," Trans. Hort. Soc. London (1847), vol. ii. p. 113.

Tulasne, "Mém. sur les Ured. et Ust.," Ann. de Sci. Nat., 4o sér., tome ii. p. 113.

¶ Bonorden, "Handb. d. Allg. Mykologie " (1851), p. 39.

** Kühn, "Krank. Kult.," 2 aufl. 1859.

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until Brefeld,* in 1882, published his investigations, by which it appears that the Ustilagineæ are capable of perpetuating themselves for long periods, outside and independently of their host-plant, in the excreta of herbivorous animals. It will be more convenient to describe the germination of the spores of the various Ustilagineæ in detail, as was done with their spore-formation.

Much confusion exists in the works of various authors who have written upon the subject, from the diverse applications to which the word "spore" has been made. For instance, Cooke † speaks of the teleutospores of the Ustilagineæ as pseudospores, which term he applies to the æcidiospores, uredospores, and teleutospores of the Uredineæ. Again, these bodies are sometimes called conidia, which term is applied by Brefeld to the secondary spores of the Ustilagineæ. In order to avoid confusion, it may as well be stated at once that while the term "spore" may be correctly applied to all the reproductive bodies possessed by these fungi, in a general sense, yet it becomes necessary to affix to it some qualifying word, such as teleuto-spore, resting-spore, uredo-spore, promycelial spore, æcidio-spore, and so forth. In speaking of the Ustilagineæ, the word " spore " has generally been applied to the perfect, lastformed bodies the teleutospores, analogous to the teleutospores of the Uredineæ; those bodies, in fact, with which we are all familiar as the black dust of bunt and smut. These black teleutospores, when they germinate, protrude a germ-tube-the promycelium. This promycelium bears certain very small hyaline bodies, which are spores, and may be fairly enough designated promycelial spores, inasmuch as they have been produced by the promycelium; as, however, the term "sporidia" is very commonly applied Brefeld, Hefenpilze." 1883.

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† Cooke and Berkeley, Fungi," International Scientific Series, vol,

xiv.

1875.

to them by Continental botanists, we may use it when writing or speaking in English.

The promycelial spores very commonly produce secondary promycelial spores by budding. Hence we may speak of primary and secondary promycelial spores. When these promycelium spores continue many times to multiply themselves by budding, after the manner of Saccharomyces, Uredine spermatia, etc., they may very well be called, as Brefeld suggests, "yeast-spores" and "yeast-colonies." The term "conidia " will be confined to that form of fruit in Tubercinia and Entyloma which is produced in the air from the mycelium in the living host-plant.

Ustilago. The germination of the spores of Ustilago varies somewhat in different species. The commonest type is that of U. segetum, violacea, maydis, kühneana, scabiosa, etc.

U. segetum.—If a few spores be placed in a drop of water, they will begin to evince signs of vitality in six or eight hours. Germination occurs more rapidly in summer than in winter, and in fresh spores than in those which have been kept some months. At one point of its surface the spore emits a germ-tube, which grows straight outwards, until it is from three to four times as long as the spore is wide; and under certain circumstances this tube may, according to Kühn, have the functions of a germtube (Plate VII. Fig. 6), entering by its pointed extremity the tissues of the host-plant. Normally, however, it becomes divided by septa into from three to five compartments, generally into four. This germ-tube is an outgrowth of the endospore, which is pushed upward through the exospore. It is from 30 to 40μ long, and from 4 to 5μ broad at its maturity. At first it is in direct communication with the endospore, and the protoplasm therein contained passes into the germ-tube and fills it. Adopting the phraseology

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