Fungi: Their Nature and Uses

by M. C. Cooke

Fig. 89.—Germinating pseudospore (g) of Tilletia caries with secondary spores in conjugation. (Tul.)

The germination of the Ustilagines was in part examined by Tulasne, but since has received accessions through the labours of Dr. A. Fischer von Waldheim.[I] Nothing, however, of any importance is added to our knowledge of the germination of Tilletia, which was made known as early as 1847.[J] After some days a little obtuse tube is protruded through the epispore, bearing at its apex long fusiform bodies, which are the sporules of the first generation. These conjugate by means of short transverse tubes, after the manner of the threads of Zygnema. Afterwards long elliptical sporules of the second generation are produced on short pedicels by the conjugated fusiform bodies of the first generation. (Fig. 89, ss.) Ultimately these sporules of the second generation germinate, and generate, on short spicules, similar sporules of a third generation. (Fig. 89, st.)

Fig. 90.—Pseudospore of Ustilago receptaculorum in germination, and secondary spores in conjugation. (Tul.)

In Ustilago (flosculorum) germination takes place readily in warm weather. The germ tube is rather smaller at its base than further on. In from fifteen to eighteen hours the contents become coarsely granular; at the same time little projections appear on the tube which are narrowed at the base, into which some of the protoplasm passes. These ultimately mature into sporules. At the same time a terminal sporule generally appears on the threads. Secondary sporules frequently grow from the primary, which are rather smaller, and these occasionally give rise to a third generation.

In Urocystis (pompholygodes) the germinating tubes spring exclusively from the darker central cells of the clusters. From these are developed at their extremity three or four linear bodies, as in Tilletia, but after this no further development has as yet been traced. It may be remarked here that Waldheim observed similar conjugation of the sporules in some species of Ustilago as have been remarked in the sporules of the first generation in Tilletia.

Fig. 91.—Conidia and zoospores of Cystopus candidus; a. conidium with the plasma divided; b. zoospores escaping; c. zoospores escaped from the conidium; d. active zoospores; e. zoospores, having lost their cilia, commencing to germinate.

Returning to Cystopus, as the last of the Uredines, we must briefly recapitulate the observations made by Professor de Bary,[K] who, by the bye, claims for them an affinity with Peronospora (Mucedines but too well known in connection with the potato disease), and not with the Uredines and their allies. In this genus there are two kinds of reproductive organs, those produced on the surface of the plant bursting through the cuticle in white pustules, and which De Bary terms conidia, which are generated in chains, and certain globose bodies termed oogonia, which are developed on the mycelium in the internal tissues of the foster plant. When the conidia are sown on water they rapidly absorb the moisture, and swell; the centre of one of the extremities soon becomes a large obtuse papilla resembling the neck of a bottle. This is filled with a granular protoplasm, in which vacuoles are formed. Soon, however, these vacuoles disappear, and very fine lines of demarcation separate the protoplasm into from five to eight polyhedric portions, each presenting a little faintly-coloured vacuole in the centre (a). Soon after this division the papilla at the extremity swells, opens itself, and at the same time the five to eight bodies which had formed in the interior are expelled one by one (b). These are zoospores, which at first take a lenticular form, and group themselves before the mouth of the parent cell in a globose mass (c.) Very soon, however, they begin to move, and then vibratile cilia show themselves (d), and by means of these appendages the entire globule moves in an oscillating manner as one by one the zoospores disengage themselves, each becoming isolated and swimming freely in the surrounding fluid. The movement is precisely that of the zoospores of Algæ.