STUDIES OF SPORE-PLANTS 263 



materials useful as human foods and in other ways, but the 

 same decay processes reduce useless organic matters to a 

 condition which makes them available for plant food. For 

 example, the vast quantities of leaves, stems, and other plant 

 materials seen in late summer must be decayed before their 

 elements can be used over again by plants, and in this 

 decay many of the decomposing fungi aid. 



Moreover, some fungi are useful because they destroy 

 insects. House-flies are sometimes seen with delicate 

 white threads projecting from their bodies. These threads 

 bear spore-cases and a mycelium grows inside the flies. 

 The spores which fall on other flies germinate, and so the 

 disease may soon become epidemic. Other similar fungous 

 diseases attack other insects, and millions of grasshoppers, 

 chinch-bugs, and other destructive species are thus killed. 

 An attempt has been made to cultivate some of these insect 

 diseases artificially in order to infect a few insects before 

 turning them loose to spread the diseases to other insects. 

 The chief difficulty is in selecting weather favorable for 

 development of the fungi. 



It should be credited to the molds that some of them 

 produce the peculiar flavors of cheeses, such as Roquefort 

 and Camembert. The manufacturers take particular pains 

 to cause the growth of almost a pure culture of the proper 

 kind of mold. 



But although some of the molds and their allies may be 

 useful from the standpoint of human interests, it must be 

 admitted that their usefulness is far overbalanced by their 

 harmfulness, especially to the numerous plants which are 

 important to the human food-supply. 



Mushrooms 



247. Molds have been studied as examples of lower 

 and simple fungi. The mushrooms are more complicated, 



