September 29, 1911] 



SCIENCE 



397 



that its neglect will be held an enduring 

 reproach to the science of our time. 



W. H. R. EiVBES 



THE NEW CHESTNUT BASK DISEASE 



In the latter part of the year 1904 Mr. H. 

 W. Merkel discovered in the Bronx Botanical 

 Garden a new and peculiar form of attack on 

 the American wild chestnut tree, Gastanea 

 dentata. Prior to the finding of the cause of 

 the infection, it had been noticed that this 

 tree seemed to be in an abnormal condition. 



A study of the infection was then under- 

 taken and cultures were successfully made. 

 It was determined, after its life history was 

 better understood, that the attack was caused 

 by a fungus, or a plant of fungoid nature, one 

 of the Pyrenomycetes, a larger order of low- 

 type plants, containing some of our most in- 

 jurious fungi. The fungi in this order are 

 known to attack not only other plants, but 

 insects. Other well-known examples of this 

 order of fungi are black knot of the plum 

 and ergot of rye. 



The chestnut blight has been identified by 

 Professor Murrill as one of the genus Dia- 

 porthe named by him parasitica, and botanic- 

 ally described in Torreya, Vol. 6, No. 9, for 

 September, 1906. Some doubt has recently 

 been thrown about the genus to which it be- 

 longs. Because of its formation of ascospores 

 within well-defined perithecia it is agreed that 

 it rightfully belongs among the Pyrenomy- 

 cetes. Its peculiar parasitic habit, however, 

 is sufficient to cast some doubt upon the desig- 

 nation of the genus. No other well-knovm 

 Diaporthe is parasitic. They are saprophytes. 

 Because of its economic importance, almost 

 vicious persistency and deadly habits with re- 

 spect to its host, the wild chestnut, it might 

 well be assigned to a new genus erected within 

 the order. For a new generic name, the idea 

 contained in the Greek NiKpwo-ts (nikrosis), a 

 slaughtering unto extinction, would not be 

 beside the fact. 



The exterior appearance of this fungus first 

 is numerous yellow pustules on the smooth 

 bark of the tree. In the deep cracks of the 



oldest bark it takes the form of yellow or 

 orange lines. Later the color turns to a much 

 deeper yellow and finally brown of deepening 

 shades. Within the pustules, the perithecia 

 are found closely clustered, sometimes ap- 

 pressed. In outline they are not unlike the 

 long-necked gourd, or a glass water-bottle. 

 The walls of the neck of a perithecium are 

 black, glistening, and, when cut across, have 

 the sheen of anthracite coal. Within the 

 perithecia are the elongated sacs or asci con- 

 taining the spores, always eight in nuniber, 

 usually arranged in two rows, glassy and some- 

 what constricted across the short diameter. 

 The largest of the asci will measure about 

 10 XSO microns ; the contained winter spores 

 sometimes as much as 5 X 10 microns. Two 

 forms of spores are found, as in many other 

 fungi. The summer spores are produced in 

 golden yellow threads protruded from the 

 dome of the pustule, usually much twisted, 

 and rarely found over a half inch in length. 

 These summer spores, with dimensions not 

 more than a fifth of those of the winter form, 

 are exceedingly minute. By abrasion, action 

 of rainfall, or other causes, they are scattered 

 about continuously during the growing season. 



It has been shown that the summer spores 

 are of a sticky, gelatinous character. They are 

 therefore peculiarly adapted to be carried 

 about on the feet of insects, squirrels, or birds. 

 Much of the heretofore inexplainable isolated 

 spot infection must be attributed to such 

 means of distribution, and less to wind action. 

 But a spore covered with minute dust particles 

 could just as easily be wind sown, as if it 

 were originally of a scarious nature. 



Entrance into a new host may be effected 

 through slight wounds in the bark, broken 

 twig ends or through insect tunnels, carried 

 there by the insect itself. It was formerly 

 believed that it entered only by these means. 

 During the survey made along the main line 

 of the Pennsylvania Railroad in the fall of 

 1910, by the Pennsylvania Department of For- 

 estry, numerous instances were found where 

 it seemed to have enacted through the lenticels 

 of the bark, without insect aid or previous 

 traumatism. It was also believed that the 



