318 



INJUKIOUS INSECTS AND FUNGI. 



[Dec. 1895. 



same in Germany, where these diseases are termed Krehs, and 

 in France, where the name is Chancre; and much confusion 

 exists generally as to the real nature of the maladies. 



There is no doubt that frost, hail, wrong and ud timely pruning, 

 and insects have injurious effects upon apple-trees, but these are 

 quite distinct. Injuries of this nature are also frequently 

 described somewhat vaguely as being due to hypertrophy, or 

 excessive sap foriDation, whereas hypertrophy may be said to be 

 the effect rather than the active cause of these troubles. A not 

 infrequent notion regarding canker is that it is due to unsuitable 

 soil, to want of drainage, or to excess, or lack, of manure, 

 or of certain manurial constituents. But cankered trees are 

 found on all soils, drained as well as undrained, and where 

 manure has been freely or sparingly applied. And it is natural 

 to find this, seeing that the real cause of canker is the very 

 dangerous fungus figured above, known as Nectria ditissima, 

 which is far more destructive tlian frost, hail, bad pruning, soil, 

 too much or too little manure. Like most other injurious fungi 

 it is difficult of detection, except by careful or trained observers. 

 Upon examination of a bough or branch infected by Nectria 

 ditissima, it will be seen that some of the twigs or shoots formed 

 are dead or dying, and that there are series of wide cracks or 

 fissures in the bark for some distance round them (A. Fig. 1), 

 and sometimes also running upwards and downwards on the 

 boughs, which are abnormally swollen near the twigs. 



Fig. 2. 



Places will be noticed in some cases upon infected trees where 

 the bark is rolled back in raised and distorted forms round the 

 back of the afiected branches, leaving the black and decaying wood 

 exposed in the middle of the circular or oval spaces denuded of 

 bark (Fig. 2). Above these, the branches are dead, partly dead, 

 or dying ; further investigation will demonstrate that there is 

 but little living wood, and that the formation of wood has been 

 for some long period disorganised, as shown by the irregularity 

 of the " annual rings." The fungus on one stem, or bough, may 

 be still living and destroying ; on another stem, or bough, it may 

 have died, but the bough, or stem, has been rendered practically 



