CHAPTER II. 



Knowledge necessary to the suggester and maker of experiments, continued. 

 States of chemical combination in which substances exist in the soil and enter 

 into plants. General composition of manures, natural and artificial. General 

 principles of husbandry. Knowledge of local practice, and of local climate. 

 Composition, functions, and nourishment of the animal body. Structure of 

 the digestive organs of different animals. General relations between the soil, 

 the plant, and the animal. How analyses are corrected, and. our knowledge 

 increased, by the perception of such relations. 



1. States of chemical combination in which substances exist 

 in the soil and enter into plants. 



IT is not enough that the substances on which plants live, exist 

 in the soil naturally or are added to it by art ; they must also 

 be present in a state in which the roots can take them up and 

 convey them into the body of the plant. 



The first condition necessary to this ready admission into the 

 roots, is solubility in water. It is believed that with the 

 exception of gases, some of which may be absorbed and enter 

 the roots, as they do the leaves, directly all bodies must be in 

 a state of solution in water before they can enter into the pores 

 of the roots. Substances, therefore, which are not more or 

 less capable of being taken up by water, are not useful in the 

 soil till they have undergone some chemical change, by which 

 a degree of solubility is imparted to them. 



Two circumstances in connexion with this point, however, 

 are deserving of being borne in mind 



1. That the quantity of water which enters the roots and 

 ascends to the leaves of a growing plant, is so great, that a 

 very small degree of solubility is sufficient, to allow of a large 

 quantity of a substance being admitted to a plant in a single 

 day. 



2. That even when a soil, upon chemical examination, yields 



