CONSIDERED WITH REFERENCE TO HORTICULTURE. 325 



gardener appropriated a quarter in the garden for the reception of these 

 trees ; had the ground thrown into wide and high ridges : on the top of these 

 ridges the trees were planted, and last summer they presented a fine healthy 

 appearance, and were well stocked with good fruit. The soil was a stiff 

 clayey loam. 



378. The gum, by which is meant an extraordinary exudation of that 

 secretion, takes place chiefly in stone-fruit trees, such as the Peach, Cherry, 

 Plum, &c., from a cut, bruise, bend, or other violent disruption 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. 



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

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

 ticularly subject to it in dry weather. Some varieties of fruit-trees are more 

 liable to mildew than others ; for instance, the Royal George and the Royal 

 Charlotte Peaches are often attacked, when other sorts, growing contiguously, 

 are free from the disease. The mildew is supposed to be produced by innu- 

 merable 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 favourable state for the appearance of the disease seems to 

 be promoted by various circumstances. It sometimes proceeds from a ten- 

 derness 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 from drawing moisture from below, 

 by injudicious surface watering. 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 cir- 

 cumstances, 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 temperature, 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 

 with a composition of water and flower 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 drought, it may frequently 

 be prevented by copiously watering the soil, by which the late Mr. Knight 



