STRUCTURE. 



37 



The angle-cells are, in this stage, triangular and nearly equilateral 

 (Fig. ii a) ; the lateral cells are narrow and brick-shaped, with their ends 

 abutting on the canals. It is largely by the great extension of the lateral 

 cells that the air-canals and the roots themselves increase in diameter ; 

 for the shortest side of the young cell becomes much the longest in 

 maturity ; meanwhile the angle-cells have expanded also, their three 

 points becoming first rounded, then flattened, to give the cell its hexagonal 

 shape (cf. Fig. 8 and 1 1). 



A diaphragm of an air-canal may be traced back (Fig. 12) to a single 

 lateral cell near the tip of the root ; this extends out into the lumen of the 

 canal, by distension of its wall, as a rounded papilla. The papilla is cut 

 off, and soon divides longitudinally ; each half then divides transversely, 

 and again longitudinally. Thus by growth a plate of cells is formed, ex- 

 tending across the 

 canal. As these 



cells enlarge, inter- T^^ V \ \^* A 1 

 cellular spaces are 

 formed between 

 them until the ma- 

 ture diaphragm is 

 produced. Stellate 

 cells develop from 

 the angle-cells in 



the USUal Way, viz., FIG. ll. Development of air-canals. Transverse section of root-tip of N. flavn- 



, , virens. From photomicrograph, a, earliest stage ; b, division of one angle-cell ; 



by extension OI the c, cell divisions nearly completed; e, epidermis; ft, hypodermal layer; (a) is 



11 i farther from apex than (b), but from the same root. 



wall at several 



points, with subsequent thickening and deposition of crystals. This is 



exactly as described for Ntiphar lutea by Trecul (1845). 



Lateral rootlets take their origin while the root tissues are still very 

 young, even within the root cap. They spring from the pericambial layer 

 opposite each xylem ray, and make their exit in the usual way, but not 

 until a considerable time after their inception ; they do not occur in a 

 mature state near to the root apex. 



THE STEM. 



Externally the stems of Nymphaeas offer some striking differences, 

 which are at times characteristic of subgenera or even of species. 

 Members of the Eu-castalia group have always a stout, spongy, horizontal 

 rhizome which decays in its older parts as it elongates by apical growth. 



