1916] 



ROBERTS— EPIDERMAL CELLS OF ROOTS 



497 



b) The chemical nature of walls i, 2, 4, 6. — It will be seen from 

 table III that a majority of the forms investigated have a wall 

 made up of two parts, an inner membrane which gives the 

 cellulose reaction with 75 per cent H,S0 4 and IKI, and an outer 

 membrane which stains red with Ruthenium red, denoting 

 pectin. That this membrane is calcium pectate is shown by the 

 fact that on the addition of ammonium oxalate the membrane 

 breaks down and calcium oxalate crystals are formed. It will be 

 seen that some forms have a third membrane at the tip of the root 

 hair. This membrane stains with all the callose stains, blue with 

 aniline blue and resorsin blue, red with corallin soda. It will be 

 noted that corn is the only form examined which has one membrane 

 and that of cellulose. 



TABLE III 



The walls 2, 4, 6, and / are alike in that they all have an inner 

 membrane of cellulose and an outer membrane of calcium pectate, 

 but differ in that the calcium pectate membrane on wall 1 is thicker, 

 and in some instances in the presence of callose at the tip of the 

 hair. The calcium pectate membrane on side 1 is continuous with 

 the middle lamella of calcium pectate of walls 2, 4, 6. There is 

 then a secretion of calcium pectate about the entire cell. 



