76 THE DISEASES AND ACCIDENTS OF PLANTS, 



Cherry, Plum, &c., from a cut, bruise, bend, or other violent disrup- 

 tion of the tissue, or by injudicious pruning; often, however, without 

 any visible cause. The gum on the young shoots of Peach-trees is 

 analogous to the canker on Apple-trees, and seems to be caused by a 

 cold wet soil, or a cold wet climate. Trees subject to this disease will 

 live many years, and bear abundantly, though sometimes they are 

 destroyed by it. For the gum we know of no remedy. 



Mildew appears in the form of a whitish coating on the surface of 

 leaves, chiefly on those of herbaceous plants and seedling trees. De- 

 ficiency of nutriment is favourable to the production of mildew ; it 

 seems also to prefer glaucous-leaved plants, as the Swedish Turnip, 

 Rape, and Peas, which are particularly subject to it in dry weather. 

 Some varieties of fruit-trees ar^ more liable to mildew than others ; 

 for instance, the Royal George and the Royal Charlotte Peaches are 

 often attacked, when other sorts, growing close by them, are free from 

 the disease. Peaches with glands are mostly exempt from mildew, 

 and ought to be planted where the disease is prevalent. The mildew is 

 supposed to be produced by innumerable plants of a minute fungus, 

 the seeds of which, floating in the air, find a suitable nidus in the 

 state of the surface of the leaf, and root into its stomata. This favour- 

 able state for the appearance of the disease seems to be promoted by 

 various circumstances. It sometimes proceeds from a tenderness in 

 plants, produced from sowing or planting too thick. It exhibits itself 

 in a season of dry weather, when the leaves become in a languid state, 

 produced often by the roots being prevented, by injudicious surface 

 watering, from drawing moisture from below. It also shows itself 

 after a season of wet weather, if the drainage is defective, and the 

 leaves have become surcharged with crude juices. More especially 

 does it present itself in either of these circumstances, when the roots 

 and branches of a plant are placed very differently relatively to moisture 

 and temperature. For instance, it is very apt to make its appearance 

 in a peach-house, if the border should be cold and wet, and the top of 

 the tree in a warm arid atmosphere. The same effect will be produced 

 when the atmosphere is genial and moist, and the border allowed to 

 become too dry. Cucumbers grown in pine stoves, will often become 

 much infested with mildew in the winter months ; because unless the 

 pines should be in fruit, they will neither enjoy the requisite tempera- 

 ture, nor a sufficiently moist atmosphere. In many cases also the 

 disease proceeds from the soil being exhausted ; from containing too 

 much inert carbonaceous matter, or becoming soured or sodden from 

 want of drainage. In such cases trees are often completely cured by 

 replanting properly in fresh soil. The best temporary specific for 

 arresting the disease, is washing the affected parts Avith a composition 

 of water and flowers of sulphur. If the plants are tender, it will be 

 advisable to shake the sulphur in a state of powder on the affected 

 parts when dry. In both cases it will be necessary to guard against 

 bright sunshine by partial shading. In some cases the labour of 

 sulphuring may be dispensed with, by at once cutting off the affected 

 leaves and shoots. Where the mildew is liable to be produced by 



