62 



Lecture 12, July 27, 1900. 

 Roots. 

 1. Absorption, 



a. Soil plants. 

 More-uniform in stnicture than stems or leaves. 



Ordinary roots much branched, ends smaller than those of steri- being 

 the root-hairs. Chief function of root-hairs is absorption of water 

 and salts in water } hence root is not organ of absorption but of 

 display. Osmosis governs the absorption of different sixbstanoes, 

 the root-hairs having the power of selective absorption, hence 

 plants have really an advantage over animals. Two functions of 

 roots are display and conduction. 



Why is there difference in size between root-hair and leaf ? 



1. It is capillary to enable it to penetrate the soil. 



2. It can come into more intimate contact with the soil particles, 

 every cell coming in touch. 



3. It has greater amount of surface in a given volume, than any other 

 form could have. 



Liverworts have no true roots, but rhizoids, which are like root- 

 hairs in function but like the root in tropisms. In mosses they 

 are more highly developed but a great gap between rhizoids of mosses 

 and roots of ferns. 



In a few land Algae like Botrydiura, we find rhizoids developed. 



b. Water Plants. 



If Indian corn is grown in water, root-hairs are lost, but many 



