11 



These two kinds of spores are different in origin but the same in 

 power in producing the young plant. For the benefit of the micro- 

 scopist it may be well to state, the winter or sac spores are sexual 

 spores and the conidial or summer spores are non-sexual. It would 

 take from five to six hundred of the tiny sacs placed end to end to 

 measure one inch and about three thousand of the sac spores end 

 to end to measure an inch, and of the minute summer spores eight 

 to nine thousand. Both kinds of spores are produced by countless 

 millions. A section of a limb twelve inches in length and one inch 

 in diameter will furnish an ample supply of spores to infect all the 

 chestnut trees in a county. The minute spores are carried by the 

 wind, on the feathers of birds and the fur of squirrels, and find a 

 lodgment where the bark is abraded and especially in the fork of the 

 limbs or more tender branches. The spore immediately sprouts, and 

 procures its nourishment from the new wood or cambium layer. 

 These newly formed wood cells have very thin delicate walls and are 

 full of sap. Thus the cambium furnishes the parasite' with ample 

 nourishment. The walls of the new wood cells are broken down by 

 the growing parasite and the bark begins to change color from a 

 healthy olive green on twigs and slender branches to a reddish brick 

 color, and the parasite shows a tendency to girdle the limb or trunk. 

 As soon as the girdle is complete, all nourishment is cut off from the 

 parts beyond the infected portion. The result is the same whether 

 the girdling is done with an axe, a saw, or by a parasite. Large 

 trees are girdled and killed in two or three years. During the sum- 

 mer of 1908 many branches of chestnut trees showed signs of decay 

 and the green leaves of spring withered long before the frosts of 

 autumn had touched the foliage. So far we have spoken only of the 

 growing fungus. Its work during this stage is carried on in and be- 

 neath the bark. It is technically speaking a hypophloeous disease. 

 The next stage is known as the fruiting j)eriod. As the fungus grows 

 it finally matures and develops the fruiting body, or rather fruiting 

 bodies. Its growth is now outward, through the pores in the bark. 

 In old trees the fruiting or s])ore producing bodies are in the long 

 crevices or fissures of the bark. A ])iece of a limb kept in the lab- 

 oratory where the changes in the weather will not affect it, will soon 

 be thickly beset with sumll yellow ])ustules, resembling little yellow 

 cu.shions of velvet. These are fruiting bodies of this i)arasite. Eun- 

 ning through the pustule are some dark lines. These are the necks 

 of the fhisks or perithecia at the base of the pustule and are situated 

 just beneath the outer layer of the bark. These flasks are lined Avith 

 the eight-.^])ored sacs. In early s])ring and during the summer the 

 thread masses consisting of the summer or conidial spores will be 

 found. These threads are dissolved and washed away by the rain 

 and the spores are blown about by the wind. These developments 



