184 LECTURES ON 



Roman civilization, to ridge up the fields by the plough, thus bringing 

 the soil into beds of a rod or thereabouts in width, which are several 

 inches higher in the centre than at the edges. It was observed that 

 in time of dry weather the plants stationed upon the centre of the 

 ridges fared best, while those at the borders were liable to suffer, 

 although it might be supposed they occupied the most favorable 

 position, so far as access to the subterranean moisture is concerned. 

 On a moment's reflection, it is obvious that the deeper the "staple" 

 or penetrable friable soil is, the greater space will be occupied by 

 the rootlets of plants, .and the larger will be the supplies of capillary 

 moisture; so that if the soil under the influence of protracted drought 

 becomes surface-dry to the depth of one inch or two inches, less in- 

 jury will accrue to the crop whose roots are diffused through a deep 

 soil than to one stationed in a shallow tilth. The fact seen in the 

 ridged fields is far more plainly exhibited on comparing drained and 

 undrained lands. In fact, drainage is recognized, among practical 

 farmers, as the best protection against drought. Not only does it 

 regulate the use of the water which falls upon the fields as rain, but 

 by exposing an immense amount of absorbent surface to the atmos- 

 phere, which freely permeates the drained soil, large quantities of 

 water are collected and condensed from the vapor of the air. It has 

 been recently observed at Hinxworth, England, that the flow of 

 water from drains sometimes increases considerably when the baro- 

 meter falls, although no rain-fall has occurred. 



The various chemical advantages that have been already attributed 

 to tillage, viz: aeration of the soil, solution and preparation of plant- 

 food, oxydation of unwholesome matters, are evidently to be antici- 

 pated from drainage in an eminent degree. In wet climates it is 

 found to be the best preparation for effectual tillage, and where the 

 condition of the soil requires it, the indispensable pre-requisite to 

 profitable husbandry. 



The tenacious and intractable characters of clay soils are also effec- 

 tually overcome by the operation of heat — by burning the clay. A 

 heat of redness expels the combined water of clay, and destroys for- 

 ever its tenacity. A part of the soil is converted into something like 

 brick-dust, and the admixture of a small proportion of this is suffi- 

 cient to amend the heaviest soils. The same burning likewise makes 

 soluble the alkalies, and, in fact, nearly all the fixed mineral matters 

 of the cla^y, thus rendering it more fertile by increasing its power of 

 feeding vegetation. 



It often happens that contiguous soils are greatly improved by 

 mixing together. A few loads of clay remedy the too great porosity 

 of a sand, and vice versa. 



The physical characters of the soil being set to rights, the next 

 point is to feed the plant. So soon as crops "fall below a certain unre- 

 munerative rate of yield, which, in most soils, happens in a few years, 

 other means of improvement, viz: manures, are called into requisition. 



We have already spoken of tillage as a substitute for manure; but 

 the word manure originally included tillage, coming from the French 



