420 



All of the groups of the mushrooms so far mentioned produce their 

 spores on basidia and are, therefore, Basidiomycetes. There is an- 

 other very large group of fungi, which includes a few mushrooms, 

 which produces its spores in a very different way. This is the group 

 of sac fungi or Ascomycetes, so called because their spores are pro- 

 duced within little sac-like structures. A great majority of the sac 

 fungi have very small fruit bodies and grow as parasites on other 

 plants. These are very important and very interesting as the causes 

 of plant diseases, but they are not mushrooms. A familiar example 

 of a mushroom belonging to this group is the morel (page 547), the 

 sponge-like mushroom which is collected for the table by so many 

 people in early spring. If we were to cut a very thin slice at right 

 angles to the surface of a morel and examine it with a microscope we 

 should find a large number of little elongated sacs, each one containing 

 eight spores. These sacs are scattered thickly over the whole surface 

 of the cap. There are several other types of mushrooms belonging to 

 the sac-fungi group, some of them edible and a few of them slightl}; 

 poisonous. The "truffles", which are so highly prized in certain 

 European countries, are sac fungi. 



The; Ecoi^ogy of Mushrooms 



By the ecology of plants we mean their relations to the environ- 

 ment in which they live. No fungus can ever go through its entire 

 life history wholly independent of other living or dead organisms, nor 

 without being greatly affected by heat, light, water, character of soil 

 or other substratum, etc. The study of these various interrelations 

 is not only extremely interesting but is necessary to a proper under- 

 standing of the life of mushrooms. 



Dissemination. — An important ecological consideration is that of 

 the methods by which the spores are scattered. As we have said, thj 

 spores are discharged forcibly, but in the case of the gill fungi, it is 

 merely to get them away from the gill so that they can fall freely, 

 and they need to be scattered by some external means. This is in most 

 cases done by the wind. The spores of a mushroom are exceedingly 

 light and the slightest air-current is enough to carrv them away. For 

 this reason very few of the spores fall below or near the fruit body 

 that produces them. Practicallv all of them are caught up by air cur- 

 rents before they reach the ground, even in the case of short-stemmed 

 mushrooms, and they may be carried by the wind for many miles. 

 This is undoubtedly the most important means of spore dissemination. 

 vSpores often stick to the bodies of slugs, and other small animals that 

 feed upon the mushrooms, and are disseminated in that way, but that 

 is a method of minor importance. 



