THE WATERLILIES. 



long thimble-like prolongation around the root. Its outer surface is 

 bounded by a distinct, smooth layer of cells, which are much larger than 

 the underlying ones (cf. Fig. 6). At the apex these outer cells are 

 columnar in shape and arrangement and are removed from the region of 

 initial cells by 12 or 13 elongated elements (columella) ; they become 

 nearly cubical opposite the initial region, where the cap is five to six cells 

 thick, and elongated in the upper free portion of the cap, where for some 

 distance this layer alone is present. 



The relative size of the root-cap in this species is shown by the 

 following measurements. The cap extends 0.035 mrn - beyond the initial 

 cells, and 1.33 mm. above this around the root; its diameter opposite 

 the initials is 0.51 mm., the same as the diameter of the root above 



the cap. A somewhat larger root-tip 

 of N. caerulea, (Fig. 6), taken from a 

 young root of a mature plant, shows a 

 structure exactly similar to that of N. 

 flavo-virens ; in one specimen, however, 

 the apical portion of the cap had been 

 worn away in irregular fashion so that 

 the primitive outer layer of large clear 

 cells is visible only on the sides. All 

 of the cells of the cap are arranged in 

 longitudinal rows. The peripheral por- 



fa) 



Fio. 7. True and false epidermis of roots. W. 



martiticea chromatella. (a) from very young, (b) tion of the Cap is COntinilOUS with the 

 older, (d) mature root in transverse section; (c) , , . j . 



surface view of (6), e, epidermis, ft, hypodermal Upper, sheathing part, and IS Composed 



of narrower cells than those below the 



body of the root. The root-meristem and root-cap are formed by a 

 transverse row of cells as described above. 



A regular epidermis of columnar cells is found near the apex of the 

 roots (Fig. 7 (a) e) ; the outer walls of these cells are cutinized, but their 

 partition walls are quite thin. They increase somewhat in size as the root 

 enlarges, but their outer ends become rounded and somewhat drawn 

 apart (Fig. 7 (6) c). In most of the species examined (IV. flava, tuberosa, 

 odorata minor, marliacea-chromatella, lotus] they become almost cubical in 

 shape (i. e., in cross section ; they are elongated in the direction of the 

 axis of the root), then are ruptured in their outer walls, the radial walls 

 remaining as a black, irregular fringe on the surface of the root (Fig. 7 (d] 

 e], giving it a powdery appearance. In A T . clegans X zansibaricnsis, the 

 epidermal cells become greatly flattened and epithelioid before rupturing. 



