MANUS A HAND. 1 03 



K 



by costly and troublesome analysis, which element is 

 missing : but we may be very sure it is one of these 

 four. If the soil is poor and the crops are light, and 

 the business of raising crops is unprofitable, some one 

 or more elements are missing, or have been eaten up 

 by previous crops ; and these elements will be these 

 same four. We need not trouble ourselves about the 

 oxygen, the silicon, the iron, and others. They will 

 look after themselves ; and we have only to consider 

 the nitrogen, phosphorus, potassium, and calcium. 

 The last, calcium or lime, is abundant in many soils, 

 and on such soils need not be considered. Where it 

 is not found naturally in the soil, it may be added. 

 How to tell whether it is needed in any soil, is purely 

 a matter of experiment, as we shall presently see. 

 This leaves only three elements, and makes the whole 

 matter very simple. 



XXI. PLANTS AS FERTILIZERS. If we pull 

 a living plant, like a pea-vine or clover, out of the 

 ground, we shall find in the stem, roots, branches, 

 flowers, or fruit, all the various elements it has obtained 

 from the soil, the water, and the air. Taken from its 

 home in the ground, the plant soon dies. It begins 

 to wither, it shrinks and shrivels up, and loses nearly 

 all its weight. If we go on drying it by placing it in 

 an oven, it loses more and more weight, and finally 

 becomes merely a mass of brittle material that readily 

 breaks up into dust. Such a green, soft plant will give, 

 when perfectly dry, only a small part of its original 

 weight or bulk. If we take this light, brittle matter, 



