PLANTS FROM AN ECONOMIC STANDPOINT 347 



velops, millions of spores are produced, which are blown 

 about by the wind. When they alight on the bark of 

 trees and sprout, they send little roots into .the tree and 

 absorb the food which is on its way to living cells. In a 

 short time the tree dies from 

 starvation. The only remedy 

 seems to be the removal of 

 infected trees. 



Molds. Experiment 78. Make 

 some marks on a piece of fresh 

 bread with a toothpick that has 

 been drawn across a piece of moldy 

 bread. Now put the piece of fresh 

 bread in a covered can or under 

 a dish away from the light and 

 observe it from day to day. 



Molds develop from spores 

 which are usually present in 

 the air. When these spores 

 fall upon a moist substance 

 which contains suitable food, 

 they send out fine, rootlike 

 threads which both cover and 

 penetrate the surface of the attacked substance. Mold 

 will grow on most common foods. When the spores fall 

 on a jar of jelly, they germinate if the temperature is 

 favorable, and soon the jelly is covered with a layer of 

 gray mold. To kill the mold spores it is only necessary 

 to heat the food to a temperature of 90 C. 



As a usual thing molds are destructive and render 

 foods unfit to eat. However certain foods, as Roquefort, 

 Camembert, and Brie cheeses depend upon the molds 

 for their characteristic flavor. 



Ohio Agricultural Experiment Station. 

 FIG. 309. Chestnut Canker. 



