278 SCIENCE OF AGRICULTURE. Part II. 



influence of such accidents are destroyed, but such as remain are ameliorated in 

 quality, and the reason is, their food is increased, because their roots, being enabled 

 to take a more extensive range, more is brought within their reach. 



1789. It is necessary, or at least advantageous, to supply food arlificially ; and hence 

 the origin of manuring. All organised matters are capable of being converted into 

 the food of plants ; but the best manure for ameliorating the quality, and yet retaining 

 the peculiar chemical properties of plants, must necessarily be decayed plants of their 

 own species. It ie true that plants do not differ greatly in their primary principles, and 

 that a supply of any description of putrescent manure will cause all plants to thrive ; 

 but some plants, as wheat, contain peculiar substances, (as gluten and phosphate of 

 lime,) and some manures, as those of animals, or decayed wheat, containing the same 

 substances, must necessarily be a better food or manure for such plants. Manuring is 

 an obvious imitation of nature, every where observable by the decaying herbage of 

 herbaceous plants, or the fallen leaves of trees, rotting into dust or vegetable mould 

 about their roots ; and by the effect of the dung left by pasturing or other animals. 



1790. Amelioration of climate is farther advantageous, in improving the qualities of 

 vegetables, by increasing or diminishing its temperature according to the nature of the 

 plant; unless, indeed, it is situated in a climate which experience and observation 

 how to be exactly suited to its nature. Hence the origin of shelter and shade, by 

 means of walls, hedges, or strips of plantation ; of sloping surfaces or banks, to 

 receive more directly or indirectly the rays of the sun ; of rows, drills, and ridges, 

 placed north and south in preference to east and west, in order that the sun may shine 

 on both sides of the row, drill, or ridge, or on the soil between rows and drills every 

 day in the year ; of soils better calculated to absorb and retain heat ; walls fully ex- 

 posed to the south, or to the north ; of training or spreading out the branches of trees 

 on these walls; of hot- walls ; of hot-beds; and finally of all the variety of hot- houses. 

 Nature suggests this part of culture, by presenting, in every ct)untry, different degrees 

 of shelter, shade, and surface, and in every zone different climates. 



1791. The regulation of moisture is the next point demanding attention ; for when 

 the soil is pulverised, it is more easily dried by the penetration of the air ; when an 

 increase of food is supplied, the medium through which that food is taken up by the 

 plant should be increased ; and when the temperature is increased, evaporation becomes 

 greater. Hence the origin of watering by surface or subterraneous irrigation, manual 

 supplies to the root, showering over the leaves, steaming the surrounding atmosphere, 

 &c. This is only to imitate the dews and showers, streams and floods of nature ; and 

 it is to be regretted that the imitation is in most countries attended with so much labor, 

 and requires so much nicety in the arrangement of the means, and judgment in the 

 application of the water, that it is but very partially applied by man in every part of 

 the world, excepting perhaps a small district of Italy. But moisture may be excessive ; 

 and on certain soils at certain seasons, and on certain productions at particular periods 

 of their progress, it may be necessary to carry off a great part of the natural moisture, 

 rather than let it sink into the earth, or draw it off where it has sunk in and injuriously 

 accumulated, or prevent its falling on the crop at all ; and hence the origin of surface- 

 drainage by ridges, and of under-draining by covered conduits, or gutters; and of 

 awnings and other covers to keep off the rain or dews from ripe fruits, seeds, or rare 

 flowers. 



1792. The regulation of light is the remaining point. Light sometimes requires to 

 be excluded and sometimes to be increased, in order to improve the qualities of vege- 

 tables ; and hence the origin of thinning the leaves which overshadow fruits and flowers, 

 the practice of shading cuttings, seeds, &c., and the practice of blanching. The latter 

 practice is derived from accidents observable among vegetables in a wild state, and its 

 influence on their quality is physiologically accounted for by th^ obstruction of per- 

 spiration, and the prevention of the chemical changes effected by light on the 

 epidermis. 



1793. Increasing the magnitude of vegetables, without reference to their quality, is to 

 be obtained by an increased supply of all the ingredients of food, distributed in such a 

 body of well pulverised soil as the roots can reach to ; of heat and moisture ; of a 

 partial exclusion of the direct rays of the sun, so as to moderate perspiration ; and of 

 wind, so as to prevent sudden desiccation. But experience alone can determine what 

 plants are best suited for this, and to what extent the practice can be carried. Nature 

 gives the hint in the occasional luxuriance of plants accidentally placed in favorable 

 circumstances, and man adopts it, and improving on it, produces cabbages and turnips 

 of half a cwt. ; apples of one pound and a half; and cabbage-roses of four inches in 

 diameter; productions which may in some respects be considered as diseased. 



1794. 2'o increase the number, imj)rove the quality, and increase the magnitude of par- 

 ticular parts of vegetables. It is necessary, in this case, to remove such parts of the 

 vegetable as are not wanted, as the blooms of bulbous or tuberous rooted plants, when 



