64 The Waterlilies. 



surrounding fundamental tissue with the looseness common to that tissue. 

 Three types of bundle may be distinguished : 



(1) The smallest bundles, Fig. 27, (a), consist of a strand of phloem, 

 with perhaps five or six sieve-tubes and a number of companion-cells, and 

 on the inner (central) side there may or may not be one or two spiral 

 elements. 



(2) Medium-sized bundles, Fig. 27, (b), like the former but larger 

 as to the amount of phloem, and accompanied on the inner side by a 

 small but extremely regular and round air-canal. 



(3) Still larger bundles, Fig. 27, (c), differing from (2) in having a 

 phloem strand on the inner side of the air-canal as well as on the outer 

 side ; the inner strand is usually smaller than the outer. 



Sometimes two air-canals intervene between the phloem strands, 

 Fig- 2 7> ("0- while in the center of a large petiole (or peduncle) there 

 may be three phloem strands about a single air-canal. The four or 

 six large peripheral bundles of the petiole usually have two phloem 

 strands and one or two canals. These air-canals are quite small, 

 scarcely visible to the naked eye, and are bounded by a very regular 

 row of clear cells, whose walls next to the lumen of the canal are 

 convex and strongly cuticularized. In very young petioles remnants 

 of spiral elements may be seen in these canals, showing that they bear 

 the same relation to the bundle as the well-known canals in the xylem 

 of monocotyls, Zea mays, etc. Where the petiole joins the leaf several 

 spirals are found at the sides of the canals, and these rapidly increase in 

 number as we approach the collar until the canal is wholly obliterated, 

 and there is, instead, a mass of spiral elements nearly or quite as large in 

 cross-section as the phloem strands. The neat wall of the canal dis- 

 appears pari passu with the encroachment of the spirals (cf. Caspary, 

 1858, p. 382, 385 ; 1888, p. 2 ; Solereder, 1898). 



The lamina of the waterlily leaf (Fig. 28) varies in size from 5 to 7 

 cm. in diameter in N. tetragona and odorata minor to 40 cm. or 60 cm. in 

 the large tropical forms. It is cleft nearly to the center where the petiole 

 is attached, and has been termed fissi-cordate. Nearly orbicular in most 

 species, it is somewhat oval in N. caerulea, and decidedly so in N. elegans, 

 pubescens, and tetragona. The margin is entire in Eu-castalia and Cha- 

 maenymphaea, slightly wavy at base in Xanthantha ; in Hydrocallis and 

 Brachyceras it varies from entire in N. amazonum and elegans to deeply 

 sinuate in N. rudgeana, ampla, flavo-virens, capensis, and zanzibariensis ; 

 in N. gigantea and the Lotos group the leaves are sinuate-dentate, with 



