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. caerulca, 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 N. eaerulta. a, air-canal: , 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. flavo-virens from a plant just breaking 

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



