THE ROOT 



III 



for instance in fig. 33 C only the lower parts of the root 

 are active ; there are no hairs higher up, and there is 

 no need for them there ; in that region they have 

 already done their work, and have exhausted the nutrient 

 substances from the hard particles of the soil. If we 

 now calculate the total surface of all the hairs, together 



Fig. 33. 



with the fibres that bear them, on the root of a wheat 

 plant during its life-time, we find that this surface is 

 almost a hundred times larger than the area of land 

 allotted in the fields to each wheat plant. If, on the 

 other hand, we calculate the volume of these hairs 

 which cover a length of nearly thirteen miles, we find 

 that they could all be packed into a vessel of the size 

 of a thimble (about 1-5 cubic centimetres). 



Thus in the root we have an organ which, especially 



