In studying all of these forms, they may be mounted, as directed for the black moulds, in dilute glycerine; but must be handled with great care, as the spores become shaken off with the slightest jar. Of the larger _Ascomycetes_, the cup fungi (_Discomycetes_) may be taken as types. The spore fruit in these forms is often of considerable size, and, as their name indicates, is open, having the form of a flat disc or cup. A brief description of a common one will suffice to give an idea of their structure and development. _Ascobolus_ (Fig. 43) is a small, disc-shaped fungus, growing on horse dung. By keeping some of this covered with a bell jar for a week or two, so as to retain the moisture, at the end of this time a large crop of the fungus will probably have made its appearance. The part visible is the spore fruit (Fig. 43, _A_), of a light brownish color, and about as big as a pin-head. Its development may be readily followed by teasing out in water the youngest specimens that can be found, taking care to take up a little of the substratum with it, as the earliest stages are too small to be visible to the naked eye. The spore fruits arise from filaments not unlike those of the mildews, and are preceded by the formation of an archicarp composed of several cells, and readily seen through the walls of the young fruit (Fig. 43, _B_). In the study of the early stages, a potash solution will be found useful in rendering them transparent. The young fruit has much the same structure as that of the mildews, but the spore sacs are much more numerous, and there are special sterile filaments developed between them. If the young spore fruit is treated with chlor-iodide of zinc, it is rendered quite transparent, and the young spore sacs colored a beautiful blue, so that they are readily distinguishable. [Illustration: FIG. 43.--_A_, a small cup fungus (_Ascobolus_), × 5. _B_, young spore fruit, × 300. _ar._ archicarp. _C_, an older one, × 150. _ar._ archicarp. _sp._ young spore sacs. _D_, section through a full-grown spore fruit (partly diagrammatic), × 25. _sp._ spore sacs. _E_, development of spore sacs and spores: i-iii, × 300; iv, × 150. _F_, ripe spores. _G_, a sterile filament (paraphysis), × 300. _H_, large scarlet cup fungus (_Peziza_), natural size.]