52 



THE VEGETATIVE FUNCTIONS OF PLANTS 



48. Relation between Root-hairs and Soil. — If young, 

 active roots are removed from the soil, thoroughly rinsed 

 in water, and examined with a compound microscope 

 at the zone of root-hairs, it will be seen that tiny par- 

 ticles of soil have adhered so closely to the cell-wall of 



Fig. 3q. — Water-hyacinth (Eichornia crassipes). Photomicrograph of 

 a longitudinal section of a root, showing the mode of origin of lateral roots 

 {i.e. endogenous), a, b, c, lateral roots; r, t, root-cap. 



the hair that they were not washed ofif; in fact, they can- 

 not be removed without tearing the hair. They appear 

 to be imbedded in the cell- wall (Fig. 42), and are firmly 

 held by pectin mucilage, resulting from a transformation 

 of the outer membrane of calcium pectate. Since pectin 

 is a water-loving colloid its importance here is recognized 

 at once, in connection with the absorption of liquids by 

 the root-hairs. 



