=Presence or Absence of Ring or Volva.=--Of the mushrooms which have stems there are four types with respect to the presence or absence of the ring and volva. In the first type both the ring and volva are absent, as in the common fairy ring mushroom, _Marasmius oreades_; in the genus _Lactarius_, _Russula_, _Tricholoma_, _Clitocybe_, and others. In the second type the ring is present while the volva is absent, as in the common mushroom, _Agaricus campestris_, and its close allies; in the genus _Lepiota_, _Armillaria_, and others. In the third type the volva is present, but the ring is absent, as in the genus _Volvaria_, or _Amanitopsis_. In the fourth type both the ring and volva are present, as in the genus _Amanita_. =The Stem is Absent in Some Mushrooms.=--There are also quite a large number of mushrooms which lack a stem. These usually grow on stumps, logs, or tree trunks, etc., and one side of the cap is attached directly to the wood on which the fungus is growing. The pileus in such cases is lateral and shelving, that is, it stands out more or less like a shelf from the trunk or log, or in other cases is spread out flat on the surface of the wood. The shelving form is well shown in the beautiful _Claudopus nidulans_, sometimes called _Pleurotus nidulans_, and in other species of the genus _Pleurotus_, _Crepidotus_, etc. These plants will be described later, and no further description of the peculiarities in form of the mushrooms will be now attempted, since these will be best dealt with when discussing species fully under their appropriate genus. But the brief general description of form given above will be found useful merely as an introduction to the more detailed treatment. Chapter XXI should also be studied. For those who wish the use of a glossary, one is appended at the close of the book, dealing only with the more technical terms employed here. [Illustration: FIGURE 3.--Agaricus campestris. Soil washed from the "spawn" and "buttons," showing the young "buttons" attached to the strands of mycelium. (1-1/4 natural size.)] CHAPTER II. DEVELOPMENT OF THE MUSHROOM. When the stems of the mushrooms are pulled or dug from the ground, white strands are often clinging to the lower end. These strands are often seen by removing some of the earth from the young plant, as shown in Fig. 2. This is known among gardeners as "spawn." It is through the growth and increase of this spawn that gardeners propagate the cultivated mushroom. Fine specimens of the spawn of the cultivated mushroom can be seen by digging up from a bed a group of very young plants, such a group as is shown in Fig. 3. Here the white strands are more numerous than can readily be found in the lawns and pastures where the plant grows in the feral state. [Illustration: FIGURE 4.--Agaricus campestris. Sections of "buttons" at different stages, showing formation of gills and veil covering them. (Natural size.)]