Usually the basidia project into cavities within the fruit-body in which the spores themselves are released as the fruit-body gradually matures--hence the name Gastero-mycetes: ‘stomach-fungi’. In a few more advanced forms, the puff-balls of temperate countries, for instance, the spores escape from these cavities through a pore or pores in the outer wall of the fruit-body, and in the stinkhorns the spores are exposed as a sticky mass because the smell of the material in which they are held is attractive to flies. In forms which have subterranean (or hypogeous p. 243) fruit-bodies there is no special opening and here the spores are dispersed by insects and small mammals. In the bird’s nest fungi the spores are enclosed in separate packets within a saucer or cup-like open structure. Recently it has been shown by examination of the microscopic structure of the fruit-bodies and spores that certain genera of the Gasteromycetes are more closely related to the agarics than many of them are between themselves. It is believed that some of the Gasteromycetes may have evolved from more familiar fungi by adaptation to arid or semi-arid conditions. Although this is not true for all the Gasteromycetes within this one group of fungi, a whole series of methods of overcoming the disadvantages connected with non-violent disposal of spores has evolved. These methods include both changes in structure and ecology; only a few have evolved a mycorrhizal relationship with higher plants. ~Lycoperdon pyriforme~ Persoon Stump puff-ball _Fruit-body_: width 20-50 mm; height 40-75 mm. _Description_: Fruit-body: more or less pear-shaped, pale brownish often with a slight hump on the top, scurfy on the outside with tiny pointed granules which soon fall off or become rubbed off by abrasion, particularly after careless handling. Stem: consisting of rather small cells and connected at the base by long, white, branched cords of mycelium which permeate the substrate. Spore-mass: white at first then greenish yellow and finally olive-brown and formed around a sterile column. Spores: small, olive, minutely warted but appearing smooth under the student microscope; 4 µm in diameter and intermixed with long, olive coloured, branched hyphal threads 4-5 µm broad and of irregular wall thickness. _Habitat_ & _Distribution_: This puff-ball grows in huge clusters on stumps and logs, or can be traced to buried pieces of wood; it occurs from summer to late autumn. _General Information_: There are several species of _Lycoperdon_ in this country, some quite small and several rather infrequent. _L. pyriforme_ is the only one which grows on wood; ‘pyriforme’ means pear-shaped and is derived from the shape of the fruit-body.