Frequently other structures, resembling somewhat the spore fruits, are found associated with them (Fig. 39, _I_, _K_), and were for a long time supposed to be a special form of reproductive organ; but they are now known to belong to another fungus (_Cicinnobulus_), parasitic upon the mildew. They usually appear at the base of the chains of conidia, causing the basal cell to enlarge to many times its original size, and finally kill the young conidia, which shrivel up. A careful examination reveals the presence of very fine filaments within those of the mildew, which may be traced up to the base of the conidial branch, where the receptacle of the parasite is forming. The spores contained in these receptacles are very small (Fig. 39, _K_), and when ripe exude in long, worm-shaped masses, if the receptacle is placed in water. The mildews may be divided into two genera: _Podosphæra_, with a single ascus in the spore fruit; and _Erysiphe_, with two or more. In the latter the archicarp branches, each branch bearing a spore sac (Fig. 41, _B_). 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_). [Illustration: 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_).