62 THE HARMONIES OF NATURE. 



earth in its immediate vicinit} 7 ", the growing spongiole gropes 

 its way farther and farther, branches out in every direction, 

 and constantly coming into contact with new portions of soil, 

 extends the territory subservient to the wants of the plant. 

 Well may we praise the beauty of the green canopy of the woods 

 and the mighty columns which bear aloft those verdant domes ; 

 but let us also pay the tribute of our admiration to those 

 humbler organs, whose incessant activity gathers in obscurity 

 and darkness the materials of the grove, which but for them 

 would never have so proudly crested the hill or so beautifully 

 diversified the plain. 



Yet the roots, although ever so well formed for providing 

 the plant with nourishment, still required the assistance of 

 peculiar physical and chemical agencies to be able to perform 

 their functions. All plants of a higher order can, as is well 

 known, thrive, only in a soil which partly consists of the remains 

 of a lower or preceding vegetation ; the stately monarch of the 

 woods rises upon the ruins of many generations of trees or 

 shrubs of a humbler growth, and the corn-field requires fertilis- 

 ing manure to be able to reward the labours of the husbandman. 

 The rain which irrigates the field, the meadow, or the wood, 

 penetrates into the ground, imbibes the soluble salts contained 

 in the vegetable mould or humus, is absorbed by the spongioles 

 of the roots, and, ascending into the vessels of the trunk and 

 branches, saturates the whole plant with nutritious substances. 

 But rain frequently falls either after prolonged intermissions, or 

 in much greater abundance than the immediate wants of vegeta- 

 tion require ; and in both cases the plants must have suffered 

 either from an insufficiency of moisture or from its excess, wash- 

 ing away the nutritious salts contained in the soil, if their healthy 

 growth, nay, their very existence, had not been protected by the 

 admirable properties of the humus. For this wonderful substance, 

 or rather mixture of mineral and vegetable substances, attracts 

 water so strongly that it not only prevents the too rapid 

 evaporation of the rain or dew, but actually condenses the 

 aqueous vapour contained in the air, and is thus enabled con- 

 stantly to renew the sources from which the thirsty plant 

 derives its sustenance. 



As may be supposed, chemical decompositions and changes 

 are perpetually going on among the substances of which every 



