PROTECTION FROM ATMOSPHERICAL INJURIES. 389 



porated 950 Ibs. of water in an hour, while the same soil and the same 

 extent of surface not pulverised, scarcely evaporated anything. 



833. Manuring. Permanent manures, such as stable dung and other 

 solid substances, are for the most part incorporated with the soil when it is 

 dug or trenched before being cropped, and it is generally thought that most 

 advantage may be obtained from them when they are deposited near the 

 surface. Temporary manures, such as soot, bone-dust, and other powders, 

 waste yeast (one of the richest of manures), and liquid manures, such as decoc- 

 tions of dung, and solutions of salts of different kinds, are most advantageously 

 applied on the surface of the ground, and to growing crops. 



XIV. Blanching. 



834. The operation of blanching, or depriving the leaves and stems of 

 plants of their green colour, is effected by excluding light from the 

 growing plant, in consequence of which it is produced without colour, and 

 without that portion of its flavour which depends on colour. The tubers 

 of potatoes are blanched naturally, because in general they are produced 

 under the surface of the soil, or they are shaded by the foliage of the plant. 

 The points of the shoots of asparagus are blanched, in Britain, by covering 

 the crowns of the plants with a stratum of light loose soil, and on the 

 Continent by the same means, or by placing covers of different kinds over 

 them, as is done in this country with the sea-kale and tart rhubarb, by the 

 use of the blanching-pot (fig. 58, in p. 143). Celery is blanched as it 

 grows, by drawing up earth so as to cover the petioles of the leaves ; and 

 this operation is performed from time to time as long as the plants continue 

 to advance in height. The leaves of the chardoon are blanched in a similar 

 manner, and sometimes by tying them round with ropes of hay or straw. 

 The interior leaves of the common cabbage, and of the cabbage-lettuce and 

 endive, are blanched naturally, but the process is sometimes heightened by 

 tying up the leaves, and sometimes by coverings. In general, perennial 

 plants in which the nutriment for the leaves of the coming year have been 

 deposited in the roots during the year preceding, such as the asparagus, 

 sea-kale, chicory, &c., may be blanched by covering them entirely either 

 with soil or some kind of utensil ; while annual plants, the leaves arid every 

 part of which is the produce of the current year, require to have the ope- 

 ration performed by degrees as the leaves advance in size, whether by tying 

 up, earthing up, or by both modes. By the operation of tying up, 

 two effects are produced : the inner leaves as they grow, being excluded 

 from the light, are blanched ; and being compressed, in proportion to their 

 number and the degree of growth which takes place after tying up, the 

 head of leaves becomes at once tender and compact. Perennial and biennial 

 plants with ramose roots may be blanched on a large scale, by placing the 

 roots in soil, in a cellar or dark room ; but this cannot be done with annual 

 plants, which must be grown in light, and blanched as they grow. Gourds, 

 cucumbers, and apples, are sometimes blanched by growing them in opaque 

 boxes or cases ; or they are grown with pale stripes, by partially covering 

 them with strips of paper or cloth, made to adhere by gum or paste. 



XV. Protection from Atmospherical Injuries. 



The great number of plants cultivated in this country, even in the open 

 air, many of them from climates very different from ours, have given rise 



