334 QUARTERLY JOURNAL 



upon, it is better that the arable surface be rather too dry than too 

 wet when moved. Because, if too dry, it may be reduced to the 

 necessary fineness by labor, and will then be in the best possible 

 state for the reception of seeds ; the interstices between the particles 

 of the soil being filled with air, amid which the imbedded seeds 

 germinate in the greatest vigor. But if the soil be too wet when 

 moved, and especially by the pressing or pushing action of the plow, 

 it acquires from the excess of water, a stale of fluidity, like mortar, 

 and settles down again so compactly that no seed laid therein can 

 be developed in a healthy condition, in consequence of the want of 

 air. 



That the contact of air to the roots of plants was always consi- 

 dered necessary, is evident from old writings ; but the fact has never 

 been so generally noticed and acted upon as it is now. The first and 

 most srtriking instance confirmatory of the opinion, was the fact of 

 large full grown ornamental forest trees having been killed by their 

 roots being too deeply covered up with earth when levelling lawns ; 

 and planters and gardeners have been long aware of the injurious 

 effects of planting as well as sowing too deep. The same individuals 

 formerly fancied that their prepared composts, for exotic or favorite 

 flowering plants, could not be too finely sifted for their reception, 

 whether in pots, or in the open ground. But slovenly or careless 

 management in these particulars showed that too much nicety of 

 execution was not at all necessary. Sifting the composts was given 

 up, and composts made up chiefly of nodules of turf, broken stone, 

 brick rubbish, etc. are substituted with evident success; and the 

 cause is obvious : when the compost is sifted, it becomes a solid 

 mass, especially after it is watered, and repulsive of all atmospheric 

 influences ; whereas among the loose materials, a considerable body 

 of air reposes, and in this the more active fibres extend themselves 

 much more luxuriantly than they do in compact soil. 



The gardener's improved practice is only another proof how much 

 a porous soil and presence of air are necessary to the roots of plants ; 

 and yet we often see the most luxuriant vegetation produced by 

 soils which are apparently very close in texture, viz. alluvial soils 

 and fertile clays. Both these descriptions of soil being composed of 

 the finest atoms, become exceedingly close and compact if undis- 

 turbed ; but when ploughed, or otherwise moved periodically, the 

 stirred portion attracts as much of the qualities of the air as suffices 

 for the following crop. It is rather remarkable that, while oak thrives 

 best on a clayey subsoil, it does not seem to affect rich alluvial land ; 

 and this I imagine to be entirely owing to its closeness of texture 

 preventing all access of air to the place of the roots. 



Aquatic plants which live entirely submerged, although defended 

 from external air, receive as much as they need from the surrounding 

 water, which always contains a notable measure, besides nutritive 

 bodies in solution, which form the pabulum of plants, whether 

 aquatic or terrestrial. 



