Book I. PRINCIPLES OF VEGETABLE CULTURE. 279 



1825. To increase the number and improve the nutritive qualities of plants, it is neces- 

 sary to facilitate their mode of nutrition, by removing all obstacles to the progress of the 

 plant. These obstacles may either exist under or above the surface ; and hence the ori- 

 gin of draining, clearing from surface incumbrances, and the various operations, as digging, 

 ploughing, &c., for pulverising the soil. Nature suggests this in accidental ruptures of 

 the surface, broken banks, the alluvial deposits from overflowing rivers, and the earth 

 thrown up by underground animals. Many of the vegetables within the 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. 



1826. It is necessary, or at least advantageotis, to supply food artificially; 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 is 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 in the decaying herbage of herbaceous plants, 

 or the fallen leaves of trees, rotting into dust or vegetable mould about their roots j and 

 in the effect of the dung left by pasturing or other animals. 



1827. Amelioration of climate by increasing or diminishing its temperature, according 

 to the nature of the plant, is farther advantageous in improving the qualities of vegetables ; 

 unless, indeed, the plant is situated in a climate which experience and observation show 

 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 di- 

 rectly 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 ; of walls fully exposed 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 varieties of hot-houses. Nature suggests this 

 part of culture, by presenting, in every country, different degrees of shelter, shade, and 

 surface, and in every zone different climates. 



1828. The regulation of moisture is the next point demanding attention. When the 

 soil is pulverised, it is more easily penetrated both by air and water ; 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, show^ering 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 labour, and re- 

 quires 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, 

 except perhaps in a small district of Italy. But moisture may be excessive ; and on 

 certain soils at certains 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 to draw it off where it has sunk in and injuriously 

 accumulated, or to prevent its falling on the crop at all. Hence the origin of surface- 

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

 ings and other coverings to keep off the rain or dews from ripe fruits, seeds, or rare 

 flowers. 



1829. The regulation of light is the remaining point. Light sometimes requires to 

 be increased and sometimes to be excluded, 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 wdld state, and its 

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

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



1830. Increase in 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 ; by additional heat and moisture ; and 

 by 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 favourable 



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