THE WATERLILIES. 



beginning in the meristem immediately back of the initial layer of cells 

 Fig. 6 a}. They appear to be without communication of any kind with 



one another, i. e., the cells 

 bounding them fit together 

 without transverse inter- 

 cellular spaces. A single 

 perforation 0.0025 mm. in 

 diameter has been observed 

 in the side wall of a canal 

 in a root of N. tuberosa, but 

 this must for the present 

 be considered exceptional. 

 At more or less frequent 

 intervals (0.127 mm. to 

 3.0 mm. for N. tubcrosa, 

 1.2 mm. to 5 mm. for N. 

 elegans X zcuizibaricnsis) 

 diaphragms lie directly or 

 obliquely across the canals. 

 A diaphragm is a very thin 

 plate of epithelioid cells 

 (0.0076 mm. to 0.013 mm. 

 thick for N. tuberosa] with 

 sinuous margins ; the pro- 

 tuberances of the margins 

 of the cells meet one 

 another, leaving spaces be- 

 tween the sinuses (Fig. 

 12 /). In N. loins the 

 cells are more even in out- 

 line, with large, round, in- 

 tercellular spaces. Thus 

 the passage of gases is 

 left practically unimpeded. 

 The walls of the canals are 

 a single cell-layer thick, and 



FIG. 8. Hoot of Zv. ooorata, transverse section. From photomicro- 

 graph ;<, rm.nants ol ri.i<k'rrais; h, false epidermis, bear Stellate Cells (idio- 



blasts) here and there. In N. tuberosa these occur about 0.32 cm. apart 

 on the average along each canal ; in N. elegans X zanzibaricnsis they are 



