THE PATH OF EVOLUTION 



Thai 1 us that appears on the surface is the reproduc- 

 tive portion, corresponding to the inflorescence of 

 flowering plants, though as far as known it is asexual. 

 When grown it consists of a fleshy, cup-shaped body, 

 like an opened umbrella. The under side thereof is 

 divided into numerous thin, knife-like plates on which 

 are the hymenium and gills, on the surface of which 

 are the spores. These are excessively small, about 

 o5 of an inch in size ; they develop into hyphae 

 when they meet with a suitable soil. For cultiva- 

 tion, the already developed masses thereof, the mycel- 

 ium, is employed, since development from the spores 

 is a slow and uncertain procedure. These fungi, like 

 all of the genus, contain much Nitrogen in their compo- 

 sition. Many varieties are edible ; upwards of three 

 hundred kinds are known to be wholesome and nutri- 

 tious. A smaller number of the family are acrid 

 and a few are highly poisonous, especially the Amen- 

 ita, which, as they roughly resemble the common 

 mushroom (Agaricus Campestris), have not unfre- 

 quently caused death by being mistakenly eaten for 

 the latter. They, as well as all the others, obtain 

 their nourishment from already existing organic mat- 

 ter. They are incapable of assimilating the mineral 

 or a3rial elements from the earth or air. 



LICHENS. When, in any part of the world, a rock 

 surface is exposed to the weather for the first time, 



232 



