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Introduction to the Study of Science 



slices of the soil. Their tender, pliant character enables them 

 practically to envelop (cf. Fig. 147) the soil particles with 

 which they come into contact, and to absorb the film of soil 

 water which covers these particles. It is nearly impossible to 

 free root hairs from the soil without tearing them from the 

 roots, unless the greatest care is exercised. 



Exercise : Root hairs. A study of root hairs, their short life, 

 their position relative to the tip of the root and to that part of the root 

 which increases in length, and other important points may be made 

 by growing such plants as wheat, radish, bean, or corn in moistened 

 blotting paper. When the roots are long enough, mark off with India 

 ink equal lengths, as one sixteenth of an inch, from the tip of the root 



to the stalk. Examine and 

 measure every day to deter- 

 mine how rapidly and where 

 the increase in length occurs. 

 Mark the extent of the root 

 covered by root hairs and their 

 position relative to the elongat- 

 ing part of the root. Note their 

 relative number at different 

 times, their length, softness and 

 delicacy, and the short life of 

 individual hairs. Note where 

 new hairs are being constantly 

 developed, and where the older 

 ones disappear. Examine with 

 a microscope both transverse 

 and longitudinal sections of 

 roots with root hairs. 



FIG. 147. A. Diagrammatic sketch of 

 part of a transverse section of root, showing 

 surface cells and their extension as root 

 hairs. Soil particles held by root hairs, s. 

 B. Typical root with root hairs. 



In Fig. 147 (A), a part of 

 a transverse section of a root 

 with root hairs at different 

 stages of development from the surface cells is represented 

 diagrammatically. The root hairs are really tube-like exten- 

 sions of the epidermal cells and contain in solution the organic 

 substances (called root-sap), which make possible the osmotic 

 absorption of soil water with its food materials. 



