68 



COLLEGE BOTANY 



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

 trate between the pp.rticles 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 



J I growth and others may be unnecessary, or even 

 I injurious to the plant. Water and more or less of 

 J these minerals are transferred fro'm cell to cell to 

 I other parts of the plant for future use by processes 

 I which will be explained later (page 162). 

 I Distribution of Roots. — Since one of the pri- 



I 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 stirface 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 or less char- 

 I / acteristic of most plants but is influenced to some 

 I / extent by the amount and distribution of soil mois- 

 ^ yi ture and food materials. The root system is very 



extensive; when a plant is pulled from the soil, 

 most of the roots are to^rn off, but if it is removed 

 Fig, 48.— Longi- very carefullv and washed, so as to retain all the 



tudinal diagram '^ - / 



ori^n°ofbranS minuto branchcs, 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. 



