EU-MYCETES. (b) BASIDIOMYCETES 453 



size. The last stages of development of mushrooms appears to 

 be rapid. This is due to the fact that the tightly packed threads that 

 compose a " button " mushroom (Fig. 387) undergo rapid exten- 

 sion, with absorption of water. The apparently fresh formation of 

 mushrooms from day to day in the fields is thus accounted for. 

 The button-mushrooms are hidden in the grass till the extension 

 takes place. 



The Mushroom as commonly known is the fruiting body, borne on 

 the nutritive mycelium. It has the usual toad-stool form, with 

 stalk or stipe bearing the hemispherical pileus (Fig. 387). As in all 

 large fungal bodies, it consists of false tissue. The hyphae composing 

 it take first a parallel course so as to form the stipe, they then diverge 

 upwards so as to form the wide-spread pileus. In the button stage 

 the margin of the pileus is connected with the stipe by a thin covering 

 of the velum ; but this is ruptured as the mushroom expands, leaving 

 a ring round the stipe. The radiating gills, which hang vertically 

 from the lower surface, are thus freely exposed. It is upon the gills 

 that the hymenial layer, bearing the basidia, is borne. The colour 

 of the gills is at first pink, but it gradually grows dark brown with age. 

 This is due to the colour of the spores (carpospores) produced in large 

 numbers all over its surface. If a young expanded pileus be laid 

 face downwards upon a sheet of paper, after a few hours a print of 

 the gills will have been traced by deposit of their spores. 



A vertical section through the gills shows that they consist of a 

 rather lax central region, which supports the more compact hymenium, 

 that completely covers their surface. It is composed of narrow 

 paraphyses which surround the more bulky basidia, the ends of which 

 project, and in the Mushroom bear each two sterigmata, with a 

 carpospore on the end of each. The number two is, however, 

 exceptional among Basidiomycetes. The basidia of the Honey-Agaric 

 are typical (see Fig. 374, p. 441). There the fusion-nucleus divides 

 into four, sterigmata are formed, and one of the nuclei squeezes through 

 the narrow channel into the carpospore which each sterigma bears. 



In the Mushroom the germination of the spores presents a diffi- 

 cult problem. It seems probable that one incident, and perhaps 

 a necessary one, is that they should pass through the alimentary 

 tract of some herbivorous animal : for the spores would naturally 

 be taken in with the grass they eat, while the Mushroom grows on 

 old pastures manured by their dung. Related Fungi do not always 

 present such difficulties, and are readily raised from spores. In the 

 case of the Mushroom no other propagative bodies are known, nor has 



