256 



PLANT PHYSIOLOGY 



substances that are insoluble or slightly soluble in water. 

 This function of the roots was discovered by Sachs in a very 

 simple experiment, which has since been adapted for demon- 



FiG. 74. — Attachment of root 

 hairs to soil particles {after 

 Molisch) . 



Fig. 75. — A radish seed- 

 ling. I, showing root hairs; 

 II, with a soil coating around 

 the roots (after Molisch). 



stration. A carefully polished marble plate is inserted hori- 

 zontally or obliquely in the soil in which plants are grown, 

 legumes being best suited for this purpose. When the roots have 

 developed and some of them have come into close contact with 



Fig. 76. — Marble plate showing traces left by roots (after Nathansohn). 



the marble plate, it is taken out and washed. On the polished 

 surface of the plate will now be seen distinctly small traces etched 

 at the points of contact with the roots (Fig. 76). 



