THE BOOT AND THE SOIL 



65 



on the hypocotyl of some of the germinating corn 

 grains. In Fig. 29 A and in Fig. 28 the parts of the 

 root bearing root-hairs are indicated by 

 the sand which adheres to these parts. It 

 is usually difficult to see the root-hairs of 

 plants growing in the natural soil, but they 

 may sometimes be discovered with the help 

 of a pocket magnifying glass by carefully 

 removing the soil particles about the 

 younger roots, when the silky network of 

 root-hairs may be seen filling the smaller 

 pores of the soil or enveloping the soil 

 particles. Fig. 30 shows a magnified root- 

 hair of the wheat plant, closely attached 

 to some particles of soil. The root-hairs 

 are able to take up water freely, even from 

 soil that does not appear very wet, be- 

 cause each soil particle is enveloped in a 

 thin layer of water (90) . Still more inter- 

 esting is the fact, that root-hairs are able 

 to dissolve mineral matters in the soil, by their excre- 

 tions, most important of which is carbonic acid, thus 

 permitting the plant to use these matters as food. 



Fig. 29. — Seed- 

 lings of turnip 

 showing root- 

 hairs. 



Fig. 30. — Tip of a magnified root-hair with adhering particles of soil. 



101. Absorption of water. — Root-hairs absorb water 

 with considerable force. It is the absorptive power of 

 the root-hairs that causes water (sap) to flow so freely 



