ROOTS AND ROOT-HAIRS. 



37 



increased by the root-hairs in proportions given in 

 the following table : 



-which sufficiently establishes the general pro- 

 position that the area of the root-surface is 

 enormously increased by these hairs. 



But this does not give us any definite idea of 

 the length of the cylinders of soil explored by 

 these surfaces, until we find that plants such as an 

 ordinary sunflower, hemp, or vegetable-marrow 

 may have roots penetrating into a cubic meter of 

 soil, in all directions, and so closely that probably 

 no volume so large as a cubic centimeter is left 

 unexplored. Clark found by actual measurement 

 that the roots of a large gourd, if put end to end, 

 extended over 25 kilometers, and Nobbe gives 

 520 meters for the roots of a wheat. Vetches 

 may go nine feet deep, and oats more than three 

 feet. The Sal, a tree of the forests of India, has 

 roots which penetrate to a depth of 50 to 60 feet. 



Some rough notion of the lengths, superficies 

 and penetrating capacities of the roots of a large 

 tree may be gathered from the above, but it is 

 doubtful whether we can form any adequate ideas 

 as to the millions of root-hairs which must be 



