RATIONAL FRUIT CULTURE. 67 



times have more than one, but if so, they are, as a rule, closely 

 related. It cannot live on any others. To this extent its 

 opportunities for harm are limited. There is no need to fear 

 that, if Apples are growing near mildewed Eoses, the disease 

 will spread to them, for the species of mildew which attacks 

 the Apple is different from that on the Eose. There are other 

 limitations to the spread of disease. The fungi which attack 

 the shoots cannot penetrate sound and healthy bark. They 

 can enter only at a wound. Hence, when a branch is cut off 

 in pruning, the wounded surface should be coated with tar. 

 Even the hardness, or softness, of the foliage may make a 

 considerable difference in the power to resist disease. When 

 plants are grown in a close atmosphere under glass, their 

 foliage is so softened that they are much more liable to be 

 attacked than others in the open air. Between those in a 

 warm, moist valley, and those on a bleak hillside, there is a 

 similar difference, though, of course, it is not so pronounced. 



THE SPORES OF PARASITIC FUNGI. 



The fact that these minute fungi develop inside the tissues 

 makes it very difficult to get rid of them without injuring the 

 plants. But, like Mushrooms, which develop under ground, 

 their mycelium spreading in all directions, and rise into the • 

 air to ripen their fruit, these fungi must also come to the sur- 

 face to ripen their spores, and, if the spores are destroyed before 

 they scatter, the infection of other trees, and of other parts 

 of the same tree, is prevented. Spores may be produced in 

 summer, and again in autumn. The latter are called resting 

 spores, because they remain dormant during the winter, start- 

 ing to grow when the temperature rises in spring. It is by 

 their means that infection is carried on from year to year. If 

 they are destroyed, the disease is stamped out, unless, as is 

 the case with some parasitic fungi, the mycelium is perennial — 

 that is, keeps on spreading among the tissues for many years. 



