CHAPTER IV 



THE ROOT 



WE saw at the end of our last lecture that during the 

 period of germination the young plant does not exhibit 

 the most characteristic feature of vegetable life, increase 

 in mass. On the contrary, in spite of a visible increase 

 in volume, it loses continually in dry weight, burning 

 away part of its substance in respiration. 



It is only when the organs become individualised and 

 begin to fulfil their natural functions, the root sinking 

 into the soil and the stem with the leaves stretching 

 into the air towards the light, it is only then that the 

 full and independent life of the plant manifests itself in 

 the real assimilation of matter from the external 

 environment. 



We know already what kind of matter is thus assimi- 

 lated : it consists of the twelve elements already 

 enumerated. We have now to settle a further question : 

 From what part of the environment does the plant obtain 

 these various substances from the soil, water, or air ; 

 and what are the means by which they enter the plant? 

 We shall learn at the same time which of the two organs, 

 the root or the leaf, is to be considered the nutritive 

 organ of the plant, or whether they both serve that 

 purpose, each in its own way. 



Let us begin with the root, since the problem seems 

 simpler in connection with this organ. Scarcely any one 

 has ever doubted the fact that the root serves the 

 purpose of nourishing the plant, and it is fairly easy to 

 prove that at least one form of nutrient substances 

 cannot penetrate into the plant otherwise than through 



