304 



STRUCTURE AND LIFE HISTORIES 



making it possible for the mycelium to penetrate with ease. 

 This process disintegrates the wood, weakens the tree so that 

 it eventually dies or is easily blown over by the wind, and 

 of course renders the wood of little or no value for timber. 

 The fungus gains admission to the tree by means of the 

 spores falling on some surface freshly exposed by trim- 

 ming the tree, by the accidental breaking of branches, 

 by the ''barking" caused by lawnmowers, and in other 

 ways; on account of the disastrous results, all such sur- 

 faces should be protected by be- 

 ing painted over as soon as a 

 branch is cut or broken off, or a 

 portion of bark removed. There 

 are many species of wood-de- 

 stroying fungi, and the financial 

 loss they cause to the lumber 

 industry, not to mention the 

 losses of beautiful shade trees 

 in lawns, parks, and streets, is 

 very considerable. 



MOLDS 



The filamentous fungi, com- 

 monly known as molds, be- 

 long to various species. The 

 black mold {Mucor mucedo) is 

 common on bread, and the blue 

 mold {Penicillium) (Fig. 224) 

 on decaying fruit and on fruit canned at home. The 

 appearance of the mold indicates that the fruit was not 

 sufficiently sterilized before the cover was screwed down 

 on the fruit jar. In fact, the entire process of canning is a 



Fig. 224. — Penicillium glau- 

 cum. h, hypha; b, basal cell; st 

 sterigma; c, spore {conidium). 



