58 THE WATERLILIES. 



of N. zanzibariensis X . In A", tetragona the subepidermal layer is 

 decidedly colloid, and in other species it may be slightly so in its inner 

 walls. These colloid tissues are of the type usually described in text- 

 books for collenchyma ; the thickenings are massed in the angles where 

 three or more cells meet, sometimes from their great amount seeming to 

 extend along the narrower sides. The appearance is often that of a group 

 of round dull bodies (the cell-cavities) in a highly refractive but homo- 

 geneous medium ; in less pronounced cases the likeness is more that of a 

 network with large knots. In Miiller's (1890) valuable classification of 

 collenchyma, Nymphaea is cited as an example of his first class, " Corner- 

 collenchyma " (Eckencollenchym), and as having the colloid matter some- 

 times convex and sometimes concave to the cell-lumen ; the latter is most 

 common, but the former may be seen in N. rubra. The greatest amount 

 of thickening occurs about the middle of the colloid zone. 



The remaining tissue of the petiole, designated already as funda- 

 mental tissue, consists of larger or smaller rounded, thin-walled cells, with 

 large intercellular spaces ; it is traversed longitudinally by numerous 

 lysigenous air-canals and by vascular bundles. In N. odorata these cells 

 are of fairly uniform size, but in N. rubra the cells bounding the air-canals, 

 and those between the canals, are much smaller than those between the 

 canal-region and the collenchyma. Many of the large fundamental cells 

 are bi-nucleate, and in N. flava and N. zanzibariensis X contain starch. 



For many years the air-canals of waterlily petioles and peduncles 

 have attracted the attention of botanists on account of their large size and 

 constant and characteristic arrangement. Thus Mackintosh (1876), 

 Parlatore (1881) and Masters (1902, a, b), as well as Planchon, Caspary 

 and others have written of them. Two principal types may be distin- 

 guished in petioles of mature plants; (i) that of Eu-castalia, with four 

 nearly equal, large canals placed in a square near the middle of the 

 petiole, two anterior and two posterior, and (2) that of Lotos, Hydrocallis 

 and Xanthantha, with two greatly predominant canals and two lesser ones 

 at each end of these (anterior and posterior). Other species, as shown in 

 the diagrams (Fig. 26), approach one or other type more or less, or show 

 intermediate conditions. Starting from such an arrangement as is shown 

 in N. tetragona (19) or gigantea (n), we can easily imagine specialization 

 leading in two directions to the well-marked types above mentioned. 

 Each canal is bounded by an even layer of small cells, with walls slightly 

 convex toward the canal, and is lined with a thick cuticular coating, whose 

 function, if the researches of Barthelemy (1874) are of weight, is to aid in 



