21 r> EGYPTIAN AGRICULTURE. 



advisable as a preliminary to briefly sketch the nature of 

 the part they play in the plant's economy. It is well 

 known that plants remove from the soil in a soluble state 

 certain substances which are necessary for their growth, 

 and that the substances so drawn upon, exist in relatively 

 small proportions. Though the total amount of any 

 ingredient present may be comparatively great, yet it must 

 be remembered that it is only that portion of it which 

 can be brought into solution which is at present capable 

 of feeding the plant, and which is in consequence known 

 as the " available part." The remainder forms a reserve 

 a part of which, by means of various agencies, may even- 

 tuallv be brought into that state of solubility which is 

 requisite before it can nourish the plant. If land, 

 therefore, be continually cropped and no efforts taken to 

 restore, in some manner, the ingredients removed, it follows 

 that it will eventually become exhausted ; it will lose its 

 productiveness. In a state of nature this does not occur, 

 a condition which we have to imitate as far as possible. 



The soil may be looked upon as the farmer's warehouse, 

 from which he continually removes material in the form 

 of crops. If this be continued without making any return, 

 it follows that in the end it will be depleted. So, if we 

 continually crop our land without making ample return 

 for what we remove, we shall as it were diminish our 

 store, and arrive at a point when the land will cease to give 

 profitable returns. The richer the soil, the longer we may 

 continue to draw upon it, but eventually the result will be 

 the same. We can, however, prevent such exhaustion from 

 taking place by giving the land an occasional rest, by 



