The Disorders of Apple and Pear Trees. 
185 
( chancre cancereux ) of apple-trees, that insidious and little understood 
malady common and fatal in many English orchards. M. Dangeard 
says canker causes grave injuries in the orchards of La Sarthe, where 
dessert apples are largely grown. Many trees are attacked, but not 
all varieties to the same extent. Those which produce cider fruit 
are not so liable to canker as those yielding dessert apples. The 
Reinettes are particularly affected, and much dead wood must be cut 
from the old trees every year ; while the young trees are deformed 
and their growth is often checked. At Chambois the Reinette de 
Bretagne and the Reinette du Canada are disappearing on account 
of canker. 
Several figures are given of stages in the growth of this disorder 
and the deformities peculiar to it upon boughs, large branches, and 
small twigs. In some of these the perithecia of the fungus, Neclria 
ditissima, which causes this injury, are distinctly shown. These, the 
organs of fructification of the fungus, are tiny red specks like minute 
beads dotted here and there upon the affected parts, and just visible 
without a glass, and can always be found where active mischief is 
going on. As M. Dangeard points out, boughs and branches may 
be found with the characteristic scars of canker upon them, but the 
fungus itself Has disappeared, and vitality is preserved in proportion 
to the circumference invaded. When, however, the whole circum- 
ference of a bough or branch has been invaded, all that part above 
the canker dies. This attack, it is shown, commences at the point 
of a bud where the tissues are delicate and have been injured and 
dried up by frost or other causes and made suitable for the fungus, 
which is able to begin its existence as a saprophyte ( i.e . an organism 
which lives upon dead or decaying substances) before it attacks the 
living tissues. After a while the skin of the twig, or branch, below 
the bud is penetrated by the fine mycelium of the fungus, though 
the characteristic red perithecia are not yet seen. Some observers, 
not finding these, conclude that the affection is not due to Nectria 
ditissima, forgetting that fungi exist at first in the fine, threadlike 
mycelial form, and do not fructify at once. In the early stages of 
the parasite a depression is noticed round the part attacked by it, 
and it is not till later on that there is any increase in the diameter 
of the twig or branch, or formation of cushion-like swellings ( hourre - 
lets). M. Dangeard holds that the fungus Nectria ditissima is 
undoubtedly the cause of canker, and cites Hartig 1 and Prillieux, 2 
who have both written able treatises in exposition of their belief. 
The following advice as to treatment for canker is given : — 
1. To avoid grafting with a cankered graft, or upon a cankered 
limb. The traces of canker may be easily perceived. Every wound 
of the skin or bark is dangerous, as it serves as a centre for the 
fungus. 
2. At the very first indication of canker all affected branches 
should be cut away and burnt. 
1 Lehrbuch der BaumkranJtheiten, von Dr. R. Hartig. Berlin, 1889. 
2 Prillieux, Societe Mycologique de France, stance de juin 1888. 
