32 



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. tuber osa, but 

 this must for the present 

 be considered exceptional. 

 At more or less frequent 

 intervals (0.127 mm. to 

 3.0 mm. for N. tuberosa, 

 1.2 mm. to 5 mm. for N. 

 elegans X zanzibariensis) 

 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. tuberosd) with 

 sinuous margins ; the pro- 

 tuberances of the margins 

 of the cells meet one 

 another, leaving spaces be- 

 tween the sinuses (Fig. 

 12 /). In jV. lotus 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 

 bear stellate cells (idio- 

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

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



Fia. 8. Root of N. odorata, transverse section. From photomicro- 

 graph ; e, remnants of epidermis ,* h, false epidermis. 



