Structure. 



29 



The root-cap is said by Henslow (1892, p. 507-8) and Van Tieghem 

 (1898) to resemble in structure that of monocotyls rather than dicotyls. 

 In N. flavo-virens and N. caerulea, however, the tip of the root agrees 

 exactly with the fourth type of structure given by De Bary (1884, p. 12), 



Fio. 6.~ Longitudinal section of root-tip of IV. caerulea. a, air-canul ; s, space 

 between root and upper portion of cap. From a photomicrograph. 



i. e., there is a transverse layer of initial cells from which all of the tissues 

 are developed (Fig. 6). Caspary and Nicolai assert that the cap continues 

 to grow only for a very short period, after which no farther addition to it 

 is made, though it is persistent, and not deciduous as in Nuphar (De Bary 

 1884, p. 413). In a root of N. flavooirsns from a plant just breaking 

 from a strong tuber, the cap is short-conical and rounded at apex, with 



