i io THE LIFE OF THE PLANT 



the root is in fact confined to the belt of hairs, which are 

 in the highest degree permeable to water, far more so 

 than the tissues composing the aerial parts of the plant. 

 The root is especially interesting to us as an organ 

 of absorption, and it is important from this point of 

 view to form some idea of its length, and also of the 

 extent of its absorbing surface. A mere glance at the 

 root of any plant which' has been thoroughly washed 

 and freed from particles of soil shows us how consider- 

 able its full length must be if all its numberless branches 

 and fibres were joined end to end. But the boldest 

 conjecture falls far short of the reality. A German 

 scientist undertook the following laborious task : provid- 

 ing himself with a pair of forceps, a measuring scale, a 

 pair of compasses, and an almost inexhaustible stock of 

 patience, he actually measured the length of a wheat 

 root down to its minutest ramifications. The result 

 obtained was astounding. It turned out that the total 

 length of the root was 520 metres. However consider- 

 able that figure may be it does not even yet represent 

 the whole length of the absorbing surface of the root. 

 As a matter of fact it is the hairs which present the 

 actual absorbing surface. Let us see how many such 

 hairs the wheat plant possesses no difficult matter in 

 round numbers. Determining under the microscope 

 how many occur on one square millimetre and then 

 multiplying this by the number of square millimetres in 

 the total surface of the root, we get approximately ten 

 million. If we multiply this number by the average 

 length of the hairs we get the enormous length of twenty 

 kilometres (twelve and a half miles). Such is the path 

 traversed by the wheat root together with all its hairs 

 in the volume of soil contained in a common flower-pot. 

 I said the path traversed by the root together with all 

 its hairs, for in point of fact this figure does not represent 

 their length at any one moment in the life of the plant. 

 All the root hairs do not work simultaneously. Thus 



