GARDENERS' CHRONICLE 



OF AMERICA 



DEVOTED TO THE SCIENCE OF FLORICULTURE AND HORTICULTURE 



ADOPTED AS THE OFFICIAL ORGAN OF 



THE NATIONAL ASSOCIATION OF GARDENERS 



Vol. XVI. 



SEPTEMBER, 19L 



No. 11. 



The Symptoms of Chestnut Tree Blight 



By F. D. Heald. 



(Continued from August issue.) 

 The chestnut blight is due to a definite species of 

 fungus which grows as a parasite in the bark and to 

 some extent in the wood uf the infected tree. This 

 fungus was first described as Diaporthe parasitica 

 Murrill, but has since been referred to Endothia para- 

 sitica (Murr.) And. It is possible to grow this fungus 

 in artificial cultures, and it has been repeatedly demon- 

 strated by inoculations into healthy trees to be the 

 cause of the disease. 



1. The vegetative body i>f Mycelium. — The blight 

 fungus grows within the bark and to some extent in 

 the wood of the affected parts, where it produces 

 strands or mats of closely appressed filaments, known 

 as the mycelium or vegetative body of the fungus. 

 In young infections on smooth-barked shoots this 

 mycelium is located just below the brown, outer, or 

 corky l)ark, and is cottony white at the advancing 

 edge, but assumes a buff tinge in the central or older 

 portions of the infection. As the infections become 

 older, the mycelium penetrates deeper and spreads out 

 at various depths in the bark, where it produces char- 

 acteristic fan-like aggregates. The fans of bufif or yel- 

 lowish mycelium are especially well developed in the 

 layers of inner bark, and finally in the cambium or 

 growing layer between bark and wood, which is thus 

 destroyed by the growth uf the fungus. After the 

 mycelium has reached the cambium and spread out in 

 that region, it enters the wood and grows throughout 

 the outer layers of sapwood. It is known to penetrate 

 at least as far as five annual rings of wood. 



2. The pysnidal stage. — After the mycelium of the 

 blight fungus has been growing for a time in the 

 bark it begins the formati(jn of fruiting pustules for 

 the production of spores. The first kinds that are pro- 

 duced are known as pycnidial pustules or stromata, 

 and they appear as minute raised papilLne scarcely 

 larger than a pin-head, and showing a yellowish or 

 orange color when they break through the bark. Each 

 pycnidia pustule shows a smooth or slightly uneven 

 outer surface and is a dense aggregate of fungous 

 tissue, generally containing one (rarely more) large, 

 lobulated cavity lined with innumerable vertical fila- 

 bodies, the pycnospores, are produced. With the ac- 

 cumulation of these in a pycnidium, the external wall 

 is ruptured and the accumulated mass of spores im- 

 bedded in mucilaginous material oozes out in the form 

 of a thread-like or flattened irregular coil, the so-called 

 "spore-horn" or tendril. ;\ single spore-horn of av- 

 erage size has been found !>> actual analysis to contain 

 as many as 115,000,000 pycnospores. 



The pycnospores have frequently been designated 

 as summer spores, but the development of pycnidia de- 

 pends largely upon the age of the lesion rather than 

 on the time or season of the year. Pycnospores are 

 produced in abundance at all times in the year when 

 temperature and moisture conditions are favorable, and 

 are washed down in large numbers from diseased 

 branches even during the warm winter rains, when 

 the spore-horns are rarely observed. 



The production of jjycnospores is not confined to 

 pustules which break through the bark of diseased 

 areas. Smaller orange or reddish superficial pycnidia 

 may be produced in large numbers on the cut end of 

 the inner bark or the outer layers of sapwood of fallen 

 logs, stumps, or wood previously affected with blight, 

 or on the inner surface of inner bark where it has split 

 away from the wood. Peeled posts and poles pre- 

 viously affected with blight will frequently show many 

 of these minute pycnidia on the diseased spots, but 

 these pycnidia are generally rather scattered. Pycnidia 

 producing large numbers of viable spores have been 

 obtained from" a wood-pile two years old. Chips or 

 fragments of diseased bark or wood that fall in damp 

 locations will produce pycnidia, so that material of 

 this sort is always a possible source of infection. 



3. The perithecial stage. — Following the production 

 of pycnidia and pycnospores, a second type of fruiting 

 jnistules containing the jierithecia makes it appearance. 

 Superficially these ]K'ritliccial pustules can be readily dif- 

 ferentiated from the p)cnidial pustules, since each one 

 shows upon its surface either a number of minute raised 

 papilL-e or a number of minute black dots, the ostiolcs 

 or openings of the perithecia or flask-like bodies buried 

 deep in the stroma. 



Each perithecial pustule is a dense aggregate of 

 fungous tissue containing 1 to 60 distinct flask-like 

 cavities, the perithecia, each of which communicates 

 with the exterior by means of a long black neck which 

 opens at the top of a surface papilla. The wall of each 

 perithecium is lined with small club-shaped cells or 

 spore-sacs, which are produced in enormous numbers 

 and give rise to the .second type of spores or ascopores. 

 There is one perithecium for each superficial papilla. 



The perithecial pustules show some differences in 

 color and external appearance depending upon their 

 age and the conditions under which they have devel- 

 oped. The papillre and the stroma may both be yel- 

 lowish or orange, or the palilte may be yellowish brown 

 to brick red on a lighter ground, or in old pustules the 

 stroma may be nearly black, with slightly lighter 

 papillse. In most cases when the perithecia are mature, 



