THE ROOT loi 



suppositions, which before seemed so probable. Cultures 

 in artificial soils as well as in solutions deprived of silica 

 have proved that quite normal specimens of cereals 

 develop even in the entire absence of silica ; a plant 

 must therefore be able to exist without silica. Further, 

 experiments on a larger scale have been made actually 

 in the open fields, the soil being manured with silicates ; 

 but these experiments gave a negative result. Plants 

 in a silicated soil were laid worse than those in untreated 

 soil. It might have been suggested that the manure 

 had not reached the plant, but analysis proved that the 

 plants had really become richer in silica. This in- 

 comprehensible result was to a certain extent explained 

 when, after the general analysis of the plant, par- 

 ticular analyses were made of its several parts. It 

 appeared then that it was the leaves and not the stem 

 or the straw which became richer in silica ; and therefore 

 the increase of silica might work rather to the detriment 

 of the plant, making it top-heavy and more liable to fall, 

 instead of contributing to its steadiness. Eventually 

 it transpired that a plant can exist without silica, and 

 that its presence has nothing to do with the firmness of 

 the straw, as was formerly believed. We shall see in 

 one of our subsequent lectures that the laying of crops 

 is to be explained by other causes, and therefore can be 

 averted by other means. 



So, then, in striking silica out of the list of the elements 

 present in the ash given in the second chapter, and by 

 substituting for it the indispensable nitrogen, we get 

 eight elements that exhaust the list of substances which 

 must necessarily be supplied to the root in order to 

 nourish the plant. Four of them — nitrogen, phosphorus, 

 sulphur, and chlorine — form acids. These acids by 

 combining in pairs with the four metals, potassium, 

 calcium, magnesium, and iron, produce four salts. 

 These four salts satisfy all the requirements of the root ; 

 they furnish all the nutrient solutions used for the 



