THE BLIGHT ON CHESTNUT TREES 



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



IX INK suninuT of i<><>5. the native 

 chestnut trees in the New York 

 Zoological I 'ark gave evidence of 

 the presence of a very destructive 

 disease. It was -o..n di-o '\etvd to IK- the 

 \\ork of a deadly fungus. I >r. \\'illiani 

 A. Murrill of the Xew York I'.oianical 

 i iarden. made a careful -tudy from 

 living tree>. twigs and pure cultures 

 and published his observations in June. 

 [906, 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- 

 sitic a. 



Botanical relations. The fungi are 

 spore-bearing plants and are regarded 

 as higher than the fresh water and 

 marine alg;e or seaweeds, and lower 

 in organixation than the mosses or 

 ferns. The fungi include such plants 

 as moulds, mildews, rusts inn plants), 

 mushrooms and yeasts. The class of 

 the fungi with which we are now om- 

 cerned are known a- the sac fungi or 

 Ascomycete-. 1 Yohably 5O.CXX) species 

 of fungi are known to science, and of 

 this number more than 15,000 species 

 belong to the sac fungi. Tin- order of 

 the Ascomycetes to which parasitica 

 belongs is termed Prenoniycetes. More 

 than in> species of l)iaporthe have 

 been described. Mo-t of these SpCClCS 

 are saproplute- that IS, they -ub-i-t on 

 'cad or decaying ti--ue-. < Mic species, 

 at least, is a parasite, and its only ho-t 

 Seems to be our native die-turn tree- 



Method of ^ro-^-tli. The -pore, car- 

 ried by the wind, on the feathers . .f a 

 bird, or in the fur of a squirrel, hud- a 

 lodgment where the bark i- abraded 

 ami immediately develop- the thread- 

 or filaments technically called myce 

 bum threads, which con-titute the v 

 tativc body ,.f the fungus. The de- 



struction begin- b\ a -pore gaining ac- 

 cess through an opening in the bark to 

 the cambium or thin-walled cells which 

 make new WOM! on one sjde and new 

 bark on the other. As the -pore 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 < ir twig, or 

 branch, i- now at the mercy of tin- 

 parasite. In one or two seasons a t 

 most the girdle is complete, and all 

 nutriment is effectively cut off from all 

 parts beyond the place of the infection. 

 The girdling is a- complete as if < .tie 

 had taken an ax or a saw. During July 

 and August of npj. and also during 

 tin- -umnier of K;uX. many branches of 

 cliestnut trees showed sign- of decay 

 and the green leaves of spring with- 

 ered long before the fro-t- ( ,f autumn 

 had touched the foliage. 15 y degrees 

 the \oung bark change. 1 it- clor from 

 an olive-green to a dull rcddi-h-brown. 

 ( >n the older tree- the discoloration of 

 the bark is not apparent, but in the 

 deep tis-ure- evidences of the presence 

 of fungus may be seen. 15 y skilful 

 tapping with a hammer, any one may 

 distinguish the dead from the living- 

 bark on the oldest trunk-. Where the 

 fungu- has been at work, the sound i- 

 a tone lo\\ cr and -omewhat muffled 

 and has not the characteristic -ouud 

 coming from the healthy bark. Tlu-rc 

 i- a dead la\ cr between the bark and 

 the \vi \ < >\ the trunk. 



|5ut there i- another Stage of growth 

 t be considered. It is the fruiting 

 Imdy. solely for the purpo-c of produc- 

 ing -pores and perpetuating the -pecies. 

 \s the fungu- grows, it aNo mature- 

 hv -ending out through the pores of 

 the bark small oval pu-tule-. Tlv 

 are the fruiting bodies or -pore-pro 

 ducing lx>die- of thi- para-ite. Kach 



585 



