162 THE BOOK OF THE ROSE cuap. 



only visible on the dying leaves by the aid of a magni- 

 fying glass, though a higher power of the microscope 

 reveals them as romid black receptacles or boxes, each 

 containing eight spores. In these minute black spots 

 on the leaves Rose mildew passes its winter sleep, unhurt 

 by all that may befall save fire or being buried deeply 

 in the ground. The sun of the following summer will 

 burst the walls of the cases, and set free the spores once 

 more. 



Collecting and destroying by fire the fallen leaves is 

 thus plainly the only mode of prevention, which in most 

 cases will probably be found impracticable, but even a 

 partial carrying out of this plan should have some effect. 

 It is impossible to say how far the sj)ores may be carried 

 by a strong wind, but probably many miles. An actual 

 stamping out of the pest is therefore I fear beyond our 

 reach. 



Preventive measures consist first in the choice of an 

 open situation : in a confined place the seeds floating in 

 the wind are more apt to drop, or to be carried round 

 and round till they do attach themselves to leaves: 

 where there is free passage for the air, the same wind 

 that brings them will take most of them farther on, and 

 only a few will find resting places. 



Draughts should be avoided : places where the wind 

 comes round a corner or even through an open door are 

 often the first to be attacked. And another point is 

 just what we should recommend to a human body 

 exposed to disease-germs: keep up the constitution 

 and general health and hardiness as much as possible. 

 Avoid drought by hoeing rather than watering if 

 practicable : see to the food supply, and avoid un- 

 healthy conditions. 



Certain Roses are peculiarly susceptible to mildew, 



