2 24 PLANT LIFE. 



Now it is certainly the case that the whole genus 

 Boletus is avoided by man because of the known 

 poisonous character of B. Satanas and others ; so 

 that, in this case, the resemblance has been of use, 

 and corresponds to quite similar cases of mimicry 

 among butterflies (see Wallace). 



The inconspicuous forms are probably visited only 

 by some insect or slug which is intended to crawl 

 over them. They also show details which are inter- 

 esting and no doubt useful. For instance, the greyish- 

 red separate little scales on A. rubescens seem useless ; 

 but if one searches for young specimens among the dead 

 leaves and grasses, it will be found that, in the young 

 state, the scales are close together, so that the hat is 

 a nondescript greyish-red, which is the colour of the 

 scales, and hence young specimens are difficult to 

 see and escape notice, whilst the mature fungus is a 

 conspicuous red, impossible to overlook. 



Certain Agarics, including eleven species of Pleurotus, 

 and other fungi, produce the so-called Phospliorescence. 

 A luminous glow is given off by some substance secreted 

 by the Fungus, and this light is supposed to attract 

 insects which distribute the spores. There are twenty- 

 five species of fungi known to possess this luminosity 

 or phosphorescence. 



In the shape of mushrooms there is also great 

 variety. The main idea of a supporting stalk elevat- 

 ing the head, with the gills underneath so that rain 

 may not injure the spores, is common to the whole 

 group. But the exact curve of the cap, and the shape 

 and thickness of the stalk show extraordinary varia- 

 tions. Some are in outline much like an umbrella ; 

 others are nearly spherical ; and a great many have a 

 small boss at the top, and then a concave line. This 



