186 [ ROSACEOUS FRUITS 



used as stock for the plum. The least resistant is 

 the cultivated plum when grown on own roots, and 

 worse when grafted on the wild plum (Prunus spinosa). 

 However the wild plum is itself fairly resistant, and 

 imparts this quality to the plum grafted upon it, if it is 

 allowed to form one or two suckers as close as possible to 

 the grafted stem, provided of course that these suckers 

 are not allowed to grow too much, and exhaust 

 the tree in their turn. The precise nature of this 

 poison is not known, but as in the case of a similar 

 disease of the fig. and of the mulberry, clusters of a 

 toadstool (Armillaria mellea Vahl.) develop at the base 

 of the decaying trunk or stump of rosaceous trees 

 which have been dead for some time, so that this 

 poison may be only the dormant mycelium of the 

 fungus still lingering on the rotten roots, or it may 

 be a chemical poison secreted by the fungus, which 

 weakens the resistance of the new trees and so 

 causes them to become an easy prey to the dormant 

 mycelium. 



As the infection of the soil has a tendency to 

 extend radially from the first tree which has succumbed, 

 it is important to remove the tree as soon as the 

 grower is satisfied that it has become too sickly to 

 hold out hopes of recovery. The larger roots should 

 be digged up and burned, and the hole made for 

 their removal should be allowed to remain open and 

 exposed to the beneficial action of the sun and the 

 air, until the time comes to replace the missing tree. 

 Dead trees should be removed at once, the roots dug 

 up and burned, and the soil carted away from other 

 rosaceous trees, and replaced by fresh soil, so that 

 the roots of the new tree may not be in contact with 

 infected soil. Disinfection of the soil can be carried 

 out, should the cartage of infected soil prove too 

 expensive, and the process consists in mixing it with 

 fresh lime in the proportion of 2 or 3 kilog. per 



