1534. The origin of the fungi may therefore happen in a twofold manner, namely, by formation from other juices, and by that of their own, which is called propagation. Still at bottom both are one in kind. 1535. Their granules or vesicles are seeds, properly sporules, which are self-developed without male polarization. DIVISION. 1536. The fungi pass moreover through stages of development, which range parallel to the vegetable classes; since it is impossible for any other organs to originate in them but such as belong to the idea of the plant. The lowest fungus can therefore change only, by endeavouring to develop in itself ducts, tracheæ, roots, and such like parts. 1537. There are accordingly as many developmental stages of the fungi as there are vegetable classes. These divisions are called _families_. 1538. The vegetable families range parallel to the classes. This law must hold good of all the classes. There are therefore in each class 16 families. An association of families upon each stage may be called an order. 1539. At first the fungus is none other than a mucus-vesicle or a small cluster of vesicles, e. g. an _uredo_ or _mildew_. Such a vesicle next becomes longitudinally extended, and includes within itself other vesicles or granules, e. g. _mould_. These mould-filaments or threads unite again so as to form a common mass, which is surrounded by an external membrane, and is then called _puff-ball_. The pulverulent granules, which were irregularly accumulated in the puff-balls, unite at length in a regular manner to constitute a trunk of varied form, as in the _ascomycetes_, e. g. _sphæriæ_. Finally, the mould-filaments with their sporules are regularly collected together in an investing membrane, which, like a puff-ball, is supported upon a stipes or stem, e. g. the sarcomycetes or _agarics_. There are therefore 5 developmental stages of the fungi, which correspond to those of the classes; viz. the parenchyma, shaft, stem, flower, and fruit; and constitute orders. 1540. Each order is resolvable again into three divisions or families, which correspond to the organs. Thus there are in each class 16 tribes or families, which obviously range parallel to the vegetable organs or classes. (Vid. Tab. B.) 1541. A tribe or family is consequently the representation of a vegetable organ within a class. 1542. The genera obey the same law; for essential differences are only conceivable through the presence of different organs. 1543. Species is in the animal kingdom that which copulates without necessity and compulsion. The same definition is applicable to plants. The species range, without doubt, according to the diversities in the individual organs themselves, which admit of a great multitude of combinations, the number of which is not as yet to be determined.