34 STUDY OF COMMON PLANTS. 



As organs of absorption, it is essential that they should 

 have a large extent of surface in contact with the soil. 

 Eoots as ^ n P u H m g U P seedlings of different sorts it is 

 organs of apparent that the total length of their roots 

 is many times that of the aerial parts, and this 

 is frequently still more striking when the earth is carefully 

 washed away so as to expose the whole root system of 

 older plants. The surface is further increased by the 

 formation of root-hairs. These are delicate, elongated 

 cells, arising from the roots back of their growing point, 

 and so numerous under favorable conditions as to give 

 them a densely hairy appearance, easily noticeable to the 

 unaided eye. By their adhesive surface the root-hairs 

 attach themselves closely to the particles of soil, and by 

 means of acid excretions aid in preparing for absorption 

 the crude food materials of the earth. These substances, 

 in solution, are then taken up and carried to the parts 

 within. It is, moreover, through the agency of the root- 

 hairs that the enormous volume of water evaporated by 

 the leaves of plants in full foliage is taken up from the 

 soil and started on its upward course. 1 



The roots of many plants, particularly those that live 

 more than a year, fulfil an important function as reservoirs 

 Eoots as f reserve materials upon which the plant draws 

 storehouses, when it begins anew its period of active growth. 

 Suitable tests show that starch and sugar are the food 

 substances most commonly stored in roots; inulin also 

 occurs, though more rarely. These and other vegetable 

 products are described in detail by Sachs in his Physiology 

 of Plants. The shape taken by roots that serve as store- 

 houses is sometimes quite characteristic. As examples 



1 Johnson, How Crops G-row, p. 243 ; Haberlandt, Physiologische 

 Pflanzenanatomie, pp. 148, 149. 



