Fig. 103.—Endogenous formation of spores in Peziza confluens. In the youngest asci there is only one nucleus (b, e); this divides into two (f); and the division is repeated so that there are 4 nuclei in c and 8 in g. These surround themselves with protoplasm and a cell-wall (h, i). The protoplasm of the mother-cell is not entirely used up.
The hyphæ of the Mycelium in some remain free, in others they are felted together and form thick strands or flat, cushion-like bodies (compare in particular the stromata of the Pyrenomycetes). Some species form sclerotia (Figs. [116], [128]).
Asexual reproduction by means of conidia is known in many species as the principal means of reproduction, and the one which affords the most rapid means of distribution. The conidia may be produced on conidiophores (Fig. [109]), in conidial-layers (Fig. [122]), and often in conidiocarps (pycnidia, Figs. [120] d, e; [123] a; [124] b.). These last occur partly as the so-called “spermogonia” (that is, pycnidia with microconidia). The conidiophores never approach the basidia.
In many species the ascospores germinate and form conidia immediately (Nectria cinnabarina, Sclerotinia, Taphrina, etc.), sometimes while they are still in the ascus and before their ejection (Taphrina, Fig. [105] a). In many instances the conidia by means of continued budding can, for a longer or shorter time, produce yeast-conidia, e.g. Taphrina. In many other cases the conidia arise from the germ-tubes of the ascospores, or at any part of the mycelium. The unripe asci of Taphrina, when placed in water, develop conidia at their apices. The Sclerotinia-species produce numerous conidia whose germination has never been observed. The formation of conidia and asci sometimes takes place on the same fruit-body. In Heterosphæria patella the conidia and asci are developed successively in the same fruit-body; in the ascocarps of Dermatea frangula and Sclerotinia sclerotiorum the formation of conidia may take place. The ascocarps frequently arise from the conidial-layers (Nectria cinnabarina, etc.). This relationship of the two forms of reproduction to each other may be explained by considering that both have descended phylogenetically from sporangia.
Sometimes chlamydospores and oidia also appear in the Ascomycetes; on germination, however, they do not, as in Protomyces, form sporangia, and on this account cannot be distinctly distinguished from conidia.
The asci are morphologically the highest form of reproduction and are always found at the close of the development of these Fungi; the accessory forms of reproduction are first developed, but a well-defined alternation of generations does not occur.
In the Ascomycetes there are more than 11,000 described species, which can be classed as follows:—
- Series 1. Exoasci. Only one order.
- „ 2. Carpoasci.
- Family 1. Gymnoascales, }
- „ 2. Perisporiales, } Angiocarpic Carpoasci.
- „ 3. Pyrenomycetes, }
- „ 4. Hysteriales, }
- „ 5. Discomycetes,} Hemiangiocarpic Carpoasci.
- „ 6. Helvellales, Gymnocarpic (?) Carpoasci.
- Additional Ascolichenes: Lichen-forming Ascomycetes.
Series 1. Exoasci.
Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and oidia. One order.