142 STATES OF THE RIVER PLATE. 



alone possess the power of taking up the minerals, alka- 

 lies, and earths the inorganic elements which enter into 

 the organism of the plant and they do this by contact 

 with the soil through which these elements have been 

 distributed in an available form ; being endowed with a 

 power of attraction and abstraction superior to that of 

 the soil, which yields up to them the matters or food 

 which is required for the formation of the stems and 

 leaves, and extension of the roots. 



The food absorbed by an individual plant is in propor- 

 tion of the root surface in contact with the soil containing 

 that food, and the development of plants is in proportion 

 to the quantity of these food matters existing in an avail- 

 able form, or due supply of moisture, heat, and sunlight, 

 and the extent of feeding ground provided for them by 

 means of the subdivision of the soil, so as to admit freely 

 of the extension of the roots. 



The soil, and the roots of plants in it, require the per- 

 meation of the atmosphere to prepare the mineral food, 

 and facilitate its assimilation with the plant. This circu- 

 lation, or permeation of the plant, is in greater or less 

 degree, as there is more or less cohesion in the soil. 



Moisture is absolutely requisite for the growth of plants ; 

 it is an essential agent in the preparation of this food in 

 the soil, and it enters into the plant, is a material agent in 

 its organisation, and a large constituent of it. An excess 

 of moisture, however, is detrimental ; wet stagnating in 

 the soil obstructs the air channels, and, so to speak, sus- 

 pends the respiration. A continuous process of respiration, 

 or circulation of the atmosphere through the soil, and of 

 absorption of moisture and its evaporation in unison, is 

 as essential in the soil as in plants and living beings. 



As a consequence of efficient tillage, the cohesion of 

 the soil is broken, its atoms are separated, and an infinity 



