236 



PRACTICAL BOTANY. 



into the radicle, and notice that they are continuous with 

 the cambium. 



14. Examine the roots of the plants that have been 

 studied for root hairs. Do you find them on the young or 

 the old parts ? How far from the tips 

 of the roots are they located ? These ^^ ^ 



hairs are the organs for the absorp- 



159 



FIG. 158. Cross section of a root. The typical structure of roots is shown ; 



also the manner in which the root hairs apply themselves to particles of 



dirt to obtain nutriment from them. (After Franke.) 

 FIG. 159. Seedling of White Mustard. A, with the dirt clinging to the root 



hairs ; B, after washing. (After Sachs.) 



tion of the plant's food from the soil. In most cases they 

 excrete an acid cell sap which dissolves the solid mineral 

 constituents of the soil and pre- 

 pares them for entrance into the 

 root hair by osmosis. 



Place a piece of highly polished 

 marble in a box, cover it with two 

 or three inches of clean sand, and 

 plant Beans and Peas in the sand. 

 Keep well watered and under f avor- 

 FIG. 160. Polished marble able conditions until the plants 

 corroded by the action have atta j ne( i considerable size. 



of the sap from root 



hairs. (After Detmer.) Then take out the marble and ex- 



