As we saw in the section devoted to Flowerless Plants in Chapter I, there are many other kinds of fungi than the familiar edible mushroom and their close relatives, the often deadly poisonous toadstools. The reproductive processes in these other fungi are fairly well understood, but they can hardly be included here. In the mold on bread, the yeast used in baking, the rust of wheat and the diseases of other plants and of animals, the individual organism is so minute that it can only be detected under the microscope. Their reproductive processes are, of course, on such a minute scale that they could be followed with profit only by those equipped to study them. They have been described in many botanical textbooks, and those interested in them should consult such books. In recapitulating the reproductive processes in cryptogamous plants the thing that distinguishes them from all flowering plants is that they bear, in some stage of their life history, a spore. From this, in the great bulk of them, a mature plant never develops. Only by the production from the spore of some contrivance for bearing male and female cells, which may, as in some seaweeds, even be on different plants, can a mating of these be accomplished, and from this union will develop the mature plant. There are many modifications of this plan, but in nearly all of them the presence of water, for the free swimming of the male cell to its mate, is essential. Just as in flowering plants and in all the larger animals, however, the reproduction of young in cryptogams is a sexual process depending on the union of male and female. While in phanerogams that process may well be spoken of as visible marriage, with all the pageantry of insects and beautifully colored flowers, in cryptogams the process is not only a hidden marriage, its ways are sometimes so secret that, even in the common mushroom, the actual mating is conjectured rather than demonstrated. THE PRODUCTION OF YOUNG PLANTS WITHOUT MATING It is so generally true in all plants that a union of male and female is necessary for the production of young, and, as we have seen in most of them, the process is so uniformly successful that still another mode of producing them seems almost unnecessary. Yet in a surprisingly large number of plants new individuals, both of flowering and flowerless plants, are regularly produced without such a union and where sexuality has nothing to do with the increase.