The appendages growing out from the wall of the spore fruit are often very beautiful in form, and the two genera given above are often subdivided according to the form of these appendages.
A common mould closely allied to the mildews is found on various articles of food when allowed to remain damp, and is also very common on botanical specimens that have been poorly dried, and hence is often called “herbarium mould” (Eurotium herbariorum).
Fig. 42.—A, spore bearing filament of the herbarium mould (Eurotium), × 150. B, C, another species showing the way in which the spores are borne—optical section—× 150. D, spore fruit of the herbarium mould, × 150. E, spore sac. F, spores, × 300. G, spore-bearing filament of the common blue mould (Penicillium), × 300. sp. the spores.
The conidia are of a greenish color, and produced on the ends of upright branches which are enlarged at the end, and from which grow out little prominences, which give rise to the conidia in the same way as we have seen in the mildews ([Fig. 42], A).
Spore fruits much like those of the mildews are formed later, and are visible to the naked eye as little yellow grains ([Fig. 42], D). These contain numerous very small spore sacs (E), each with eight spores.
There are numerous common species of Eurotium, differing in color and size, some being yellow or black, and larger than the ordinary green form.
Another form, common everywhere on mouldy food of all kinds, as well as in other situations, is the blue mould (Penicillium). This, in general appearance, resembles almost exactly the herbarium mould, but is immediately distinguishable by a microscopic examination ([Fig. 42], G).
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.