CHAPTER IX. THE THALLOPHYTA. 327 



supported on a central stalk ; but sometimes the latter is inserted 

 to one side of the centre, or in a few species is altogether want- 

 ing. The most distinctive features of the group, however, con- 

 sist in the structure of the hymenium, which is composed of 

 lamelliform bodies, or " gills," as they are often called, arranged 

 in a radial manner on the under surface of the expanded portion 

 of the sporocarp or pileus. Many of the stalked forms are, in 

 the early stage of their development, invested with a membrane 

 called a velum or veil, which, at a later period, is ruptured ; but 

 its parts usually remain in the mature sporocarp, forming a 

 sheath at the base of the stalk, or a ring around it higher up, or 

 fringing the border of the pileus. Other forms are destitute of 

 the membrane. 



The species are numerous, many of them edible, others use- 

 less for food, and still others highly poisonous. Some, as the 

 genus Coprinus, produce a very perishable sporocarp, others are 

 hard, leathery and enduring. The genus Lactarius is distin- 

 guished from the rest, and from most other thallophytes, by pos- 

 sessing a milky juice. 



Among the edible species are Agaricus compestris, A. delici- 

 osus, Cantharellus cibarius, Marasmius oreades, Lactarius delici- 

 osus and Coprinus comatus ; and among the poisonous ones, 

 Agaricus muscarius and Lactarius torminosus, rank as the most 

 dangerous. 



For further illustration of the group, we may select Agaricus 

 compestris. A mass of mycelium is formed by the germinating 

 spores in the vegetable mould or humus, from which the plant 

 absorbs its food. On this, protuberances of a rounded or nodu- 

 lar form sooner or later make their appearance and rise above 

 the soil. These are the young sporocarps still invested in their 

 membrane. Presently the membrane ruptures, exposing an 

 upright stalk composed of compactly arranged hyphs, which 

 are continued at the top into the pileus. The latter is convex 

 and nearly smooth above, and the numerous radiately arranged, 

 plate-like gills, cover the concave surface below. The gill sur- 

 faces are composed partly of large sterile cells, and partly of 

 basidia, and each of the latter bears two spores. The spores 

 are minute ; and the aggregate number produced by a sporocarp 

 is enormous. 



