54 THE VEGETATIVE ORGANS 



The root-hairs are often of considerable length, and their 

 form and number very greatly affect the absorbing power 

 of a plant, e. g. the root-hairs of Maize increase the surface 

 of the root five and a half times ; while those of Barley 

 increase the surface twelve times. In some plants with 

 very small leaves (e. g. Heaths) few or no root-hairs are 

 formed ; and in many water-plants they are absent or 

 nearly so, for these plants are able to absorb water through 

 the general surface of the epidermis, not only of the root 

 but often of the shoot as well ; but most plants depend 

 for their supply of water and mineral food on the absorbing 

 activity of the root-hair region. 



The Food absorbed by a Root 



Soil-organisms and their work. Ordinarily the soil in 

 which the roots of plants grow is a very complex mixture 

 of substances solid, liquid, and gaseous ; inorganic and 

 organic ; living and dead ; animal and vegetable. Myriads 

 of tiny organisms find a home there, and also bigger ones 

 such as earthworms and the larvae of many insects. These 

 feed upon the living and dead materials in the soil, reducing 

 them into simpler compounds, breaking the soil itself into 

 a finely divided state, so that eventually a number of sub- 

 stances are brought into solution which are essential to the 

 food of a green plant. The organisms, however, differ 

 much in their usefulness in this respect ; earthworms are 

 great ploughers and pulverizers of the soil, and minute 

 organisms, like bacteria, are valuable or even indispensable ; 

 but others prey upon them and, by reducing their numbers 

 and therefore their usefulness, retard the formation of 

 soluble food-materials, thus rendering more and more 

 difficult the sustenance of plants. But these foes in turn 

 are checked by others, and so this complex society of inter- 

 dependent and ever-changing members is actively at work 

 reducing the complex materials and preparing from them 



