68 COLLEGE BOTANY 



the materials which are dissolved in it, by osmosis. They pene- 

 trate between the particles of soil and are in contact with the 

 soil water in which many minerals are dissolved (Fig. 46). 

 Some of these minerals may be necessary for 

 growth and others may be unnecessary, or even 

 injurious to the plant. Water and more or less of 

 these minerals are transferred from cell to cell to 

 other parts of the plant for future use by processes 

 which will be explained later (page 162). 



Distribution of Roots. Since one of the pri- 

 mary functions of roots is the taking in of water 

 nd other food materials, they must be distributed 

 in the soil in such a manner as to perform this 

 function to the best advantage. Some plants may 

 be called shallow feeders and have their root sys- 

 tems spread out near the surface of the soil, while 

 other plants are deep feeders and have their root 

 systems extending down deep into the soil. The 

 distribution of the root system is more\r less char- 

 acteristic of most plants but is influenced to some 

 extent by the amount and distribution of soil mois- 

 ture and food materials. The root system is very 

 extensive; when a plant is pulled from the soil, 

 most of the roots are torn off, but if it is removed 

 FIG. 48. Longi- ver y carefullv and washed, so as to retain all the 



tudinal diagram 



originof br 8 S* minute branches, the total length may amount to 

 several hundred yards. The distribution and, ex- 

 tent of the root system will receive further consideration in 

 Chapter XIII. 



