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 
FIG. 224PenicMiumgiau- 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 
cum. h, hypha;&, basal cell; st, 
sterigma; c, spore (conidium). 
