Book I. ORIGIN OF VEGETABLE CULTURE. 215 



All that is necessary, therefore, for effecting this branch of culture, is to imitate the habit- 

 ation, and to propagate. This is, or ought to be the case, wherever plants are grown for 

 medical or botanical purposes, as in herb and botanic gardens. Nature is here imitated 

 as exactly as possible, and the result is productions resembling, as near as possible, those 

 of nature. 



1006. To increase the number and improve the qualities of plants, it is necessary to faci- 

 litate 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 origin of drain- 

 ing, clearing from surface-incumbrances, and the various operations, as digging, plough- 

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

 surface, broken banks, the alluvial depositions 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 tlieir roots, being enabled to take a more extensive 

 range, more is brought within their reach. 



1007. It is necessary, or at least advantageous, 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 ma- 

 nures, as those of animals, or decayed wheat, containing the same substances, must neces- 

 sarily 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 fal- 

 len 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. 



1008. Amelioration of climate is farther advantageous, in improving the qualities of vege- 

 tables, by increasing or diminishing its temperature according to the nature of the plant • 

 unless, indeed, it be 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 directly or 

 indirectly the rays of the sun ; of soils better calculated to absorb and retain heat • 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 variety 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. 



1009. 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 «reater. 

 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 re- 

 gretted 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 un- 

 der-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. 



1010. The regulation of light is the remaining point. Light sometimes requires to be ex- 

 cluded and sometimes to be increased, in order to improve the qualities of vegetables • 

 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 in- 

 fluence on their quality is physiologically accounted for by the obstruction of perspiration, 

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



1011. 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 ex- 

 clusion 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 earned. Nature gives thphint in 



P 4 r 



