THE BLIGHT ON CHESTNUT TREES 



By JOHN MICKLEBOROUGH, Ph.D,, Brooklyn, N, Y, 



IN THE summer of 1905. the native 

 chestnut trees in the New York 

 Zoological Park gave evidence of 

 the presence of a very destructive 

 disease. It was soon discovered to be the 

 work of a deadly fungus. Dr. William 

 A. Murrill of the New York Botanical 

 Garden, made a careful study from 

 living trees, twigs and pure cultures 

 and published his observations in June, 

 1906, and in September of that year 

 gave a scientific description, placing the 

 fungus under the genus Diaporthe and 

 from its characteristic habit this new 

 species was appropriately named para- 

 sitica. 



Botanical relations. — The fungi are 

 spore-bearing plants and are regarded 

 as higher than the fresh water and 

 marine algae or seaweeds, and lower 

 in organization than the mosses or 

 ferns. The fungi include such plants 

 as moulds, mildews, rusts (on plants), 

 mushrooms, and yeasts. The class of 

 the fungi with which we are now con- 

 cerned are known as the sac fungi or 

 Ascomycetes. Probably 50,000 species 

 of fungi are known to science, and of 

 this number more than 15,000 species 

 belong to the sac fungi. The order of 

 the Ascom3xetes to which parasitica 

 belongs is termed Prenomycetes. More 

 than no species of Diaporthe have 

 been described. ^lost of these species 

 are saprophytes — that is, they subsist on 

 dead or decaying tissues. One species, 

 at least, is a parasite, and its only host 

 seems to be our native chestnut trees. 



Method of grozvth. — The spore, car- 

 ried by the wind, on the feathers of a 

 bird, or in the fur of a squirrel, finds a 

 lodgment where the bark is abraded 

 and immediately develops the threads 

 or filaments, technically called myce- 

 lium threads, which constitute the vege- 

 tative body of the fungus. The de- 



struction begins by a spore gaining ac- 

 cess through an opening in the bark to 

 the cambium or thin-walled cells which 

 make new wood on one side and new 

 bark on the other. As the spore de- 

 velops beneath the bark, there are in- 

 numerable thread-cells which grow up 

 and down and especially around the 

 branch or trunk. The tree, or twig, or 

 branch, is now at the mercy of the 

 parasite. In one or two seasons at 

 most the girdle is complete, and all 

 nutriment is effectively cut ofif from all 

 parts beyond the place of the infection. 

 The girdling is as complete as if one 

 had taken an ax or a saw. During July 

 and August of 1907, and also during 

 the summer of 1908, many branches of 

 chestnut trees showed signs of decay 

 and the green leaves of spring with- 

 ered long before the frosts of autumn 

 had touched the foliage. By degrees 

 the young bark changed its color from 

 an olive-green to a dull reddish-brown. 

 On the older trees the discoloration of 

 the bark is not apparent, but in the 

 deep fissures evidences of the presence 

 of fungus may be seen. By skilful 

 tapping with a hammer, any one may 

 distinguish the dead from the living 

 bark on the oldest trunks. Where the 

 fungus has been at work, the sound is 

 a tone lower and somewhat muffled 

 and has not the characteristic sound 

 coming from the healthy bark. There 

 is a dead layer between the bark and 

 the wood of the trunk. 



But there is another stage of growth 

 to be considered. It is the fruiting 

 lx)dy. solely for the purpose of produc- 

 ing spores and perpetuating the species. 

 As the fungus grows, it also matures 

 by sending out through the pores of 

 the bark small oval pustules. These 

 are the fruiting bodies or spore-pro- 

 ducing bodies of this parasite. Each 



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