518. Of the Moulds, one of the commoner is the Bread-Mould (Fig. 587). In fruiting it sends up a slender stalk, which bears a globular sac; this bursts at maturity and discharges innumerable spores. The blue Cheese-Mould (Fig. 588) bears a cluster of branches at top, each of which is a row of naked spores, like a string of beads, all breaking apart at maturity. Botrytis (Fig. 589), the fruiting stalk of which branches, and each branch is tipped with a spore, is one of the many moulds which live and feed upon the juices of other plants or of animals, and are often very destructive. The extremely numerous kinds of smut, rust, mildew, the ferments, bacteria, and the like, many of them very destructive to other vegetable and to animal life, are also low forms of the class of Fungi.[1] [Illustration: Fig. 587. Ascophora, the Bread-Mould. 588. Aspergillus glaucus, the mould of cheese, but common on mouldy vegetables. 589. A species of Botrytis. All magnified.] FOOTNOTES: [1] The "Introduction to Cryptogamous Botany," or third volume of "The Botanical Text Book," now in preparation by the author's colleague, Professor Farlow, will be the proper guide in the study of the Flowerless Plants, especially of the Algæ and Fungi. SECTION XVIII. CLASSIFICATION AND NOMENCLATURE. 519. Classification, in botany, is the consideration of plants in respect to their kinds and relationships. Some system of Nomenclature, or naming, is necessary for fixing and expressing botanical knowledge so as to make it available. The vast multiplicity of plants and the various degrees of their relationship imperatively require order and system, not only as to _names_ for designating the kinds of plants, but also as to _terms_ for defining their differences. Nomenclature is concerned with the names of plants. Terminology supplies names of organs or parts, and terms to designate their differences. § 1. KINDS AND RELATIONSHIP. 520. Plants and animals have two great peculiarities: 1st, they form themselves; and 2d, they multiply themselves. They reproduce their kind in a continued succession of 521. =Individuals.= Mineral things occur as _masses_, which are divisible into smaller and still smaller ones without alteration of properties. But organic things (vegetables and animals) exist as _individual beings_. Each owes its existence to a parent, and produces similar individuals in its turn. So each individual is a link of a chain; and to this chain the natural-historian applies the name of