ROOTS 



91 



absorb moisture from them. By these root liairs the aljsorb- 

 ing surface, and hence the amount of al)sor}(tion, is greatly 



increased. Individual 

 root hairs do not last 

 very long, but new 

 ones are constantly ap- 

 jiearing just behind the 

 advancing root tips, 

 and the old ones are 

 as constantly disap- 

 pearing. 



(1) Geofrojjism and 

 liydrotrojiisiii . — ^lany 

 outside influences affect 

 roots in the direction 

 of tiicir growth, and 

 as soil roots are espe- 

 cially favorable for ob- 

 serving these influ- 

 ences, two prominent 

 ones may be mentioned. The influence of gravity, or the 

 earth influence, is very strong in directing the soil root. 



Fif:. S"). Appurntns to stiow tlio ri-*priiis;f 

 to \\at(T {h3-drotro})isni) upon the part of 

 roots. The ends {«) of the box ha^'e hooks 

 for hanging, while the box proper is a cylinder 

 or trough of wire netting and is filled with 

 damp 8a\vdust. In the sawdust are planted 

 peas {g), whose roots (/;, i, t, in) first descend 

 until they emerge from the damp sawdust, 

 but soon turn back to\vard it. — After Sachs. 



Fig. 86. A raspberry plant, whose stem has been bent down to the soil and has " struciv 

 root.'' — After Beal. 



