90 



PLANT STUDIES 



by numerous thread-like processes spreading in every direc- 

 tion than by flat, expanded processes. 



It should also be noted that as soil roots are suljterra- 

 neaii they are used often for the storage of food, as in the 

 case of many sul)teri-anean stems. Certain prominent root 

 types may he noted as follows : 



(;4. Soil roots.— These roots push into the ground witli 



great energy, 

 . / \ \( '^^'^ their 



alv 

 s r I3 i n g s u r - 

 faces are en- 

 tirely covered. 

 Only the yoniig- 

 est parts of a 

 root system 

 absorb actively, 

 the older parts 

 transporting 

 the absorl)ed 

 material to the 

 stem, and liel})- 

 iug to gri]) the 

 soil. The soil 

 root is the most 

 common root 

 t y p e , li e i n g 

 used 1)y tlie great majority of seed plants and fern jjlants, 

 and amojig the moss plants the very simple root-like pro- 

 cesses are mostly soil-relat(Ml. To such roots the water of 

 tlie soil ])resents itself cither a^ free wafer — that is, water 

 that can be drained away — or as films of wafer adhering to 

 each soil particle, often called ivater of ndJiesimi. To come 

 in contact with this water, imt tmly does tlu' roof system 

 usually branch profusely in every direction, but the youngest 

 branches develop abundant absorbing hairs, or roat hairs 

 (see Fig. 84), which crowd in among the soil particles and 



— ^3— s-^JJLa^ 





FiG. SI. Knot tips of corn, Hhowiiig root hairs, their position 

 ill refcrf'iicu to the growing tip, and the effect of tlic 

 surrounding mediiun upon tlieir development : 1, in soil ; 

 2, in air ; :i, in water. 



