70 



ROOTS 



various mineral substances, — lime, potash, iron, silica, and many 

 others, — a considerable amount of organic material. Acids of 

 various kinds are present in the soil. These acids so act upon 

 certain of the mineral substances that they become dissolved in 

 the water which is absorbed by the root hairs. Root hairs also give 

 off small amounts of acid, which assist in dissolving minerals. An 

 interesting experiment may be shown to prove this. A solution of 



phenol phthaVein loses its color when an 

 acid is added to it. If the roots of a 

 growing pea are placed in a tube con- 

 taining some of this solution, very 

 sUghtly alkaline, the latter will soon 

 change from a dehcate pink to a color- 

 less solution. 



It is eas3^ to ssly that the delicate root 

 hairs absorb water, but it is much more 

 difficult to understand the process, be- 

 cause it involves the understanding of 

 certain physical phenomena. But since 

 absorption is a process common to both 

 plants and animal cells and is of vitsl 

 importance, let us study it carefully. 



Diffusion. — We all know that certain 

 substances, such as the odor of tobacco 

 smoke or the perfumes of flowers, pass 

 rapidly from the point where they are 

 given off and tend to spread in all direc- 

 tions through the air. The odor of the orange blossoms in California 

 is a memor}' to those who have driven near the orange groves. 

 Substances which will dissolve in liquids will also diffuse through 

 the liquids. A httle powdered e'osin placed in a glass of water will 

 soon make a glass of red ink, so completely does the eosin become 

 dissolved and diffused through the liquid. In the diffusion of 

 both gases and liquids particles of the substance pass from the 

 place where they are most concentrated to where they are less 

 concentrated, or lacking, the rate of travel being much slower 

 in Hquids than in gases. 



Imbibition. — The passage of water from point to point by 



Effect of root hairs on phe- 

 nolphthalein solution. The 

 change of color indicates the 

 presence of acid. 



