THE ROOT 113 



If the root fibres with their hairs were introduced into 

 a glass tube with this internal diameter, the hairs 

 would touch the wall of the tube.^ Therefore if all the 

 fibres of the root were distributed quite uniformly in the 

 soil allotted to them, every fibre would occupy just a 

 cylinder of soil, pierced through in all directions by its 

 hairs ; and, consequently, the greatest distance of a 

 particle of the soil from a root hair would be equal to 

 half the distance between the neighbouring hairs of the 

 same root ; this would be something like one-fifteenth of 

 a millimetre. This calculation gives us therefore the 

 greatest distance from which our average fibre must 

 obtain its food, and it gives us an idea of the close 

 contact into which a root comes with the hard particles 

 of the soil. Obviously it is not ev6ry root fibre that finds 

 itself in such favourable conditions. I repeat, this is 

 only a statistical average giving us a clear illustration 

 of the perfect absorbing powers of the root. This 

 adaptation is the more perfect in that the root becomes 

 specially developed in those parts of the soil where it 

 finds the most nutrient substances. This fact has been 

 proved in the following way. A plant was grown in a 

 flower-pot filled with alternate layers of fertile and 

 sterile soil. Roots developed very luxuriantly in the 

 fertile soil, but only poor and meagre fibres were pro- 

 duced in the sterile soil. This fact together with the 

 great length of the hairs seems to indicate that roots 

 must themselves go in search of their food, and that the 

 liquid food furnished to them by means of water is 

 generally inadequate. This supposition apparently 

 finds confirmation in the fact that roots of plants grown 

 in solutions or in soil submerged in water have very few 

 hairs, if any at all ; and yet the plants do not seem to 

 suffer. It is, therefore, sufficiently evident that nutrient 

 substances in a liquid medium penetrate the root very 



^ During the lecture this fact was illustrated by means of a lamp glass 

 and its brush. 



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