56 The Waterlilies. 



N. odorata and lotus, polygonal and with extremely minute intercellulars in 

 N. flava. In thickness this parenchyma reaches about eleven cells next 

 to the petiole in A^. lotus, tapering to one cell at the margin ; N. flava 

 has about 9 cells in thickness at the ridges ; N. odorata has 16 cells at 

 the ridges, and throughout its tissues are many very thin-walled, two- 

 pointed or variously forked idioblasts. Numerous small starch grains 

 were observed in the parenchyma of a young stipule of N. lotus. In 

 this species also the stipules are much more prominent when young than 

 on mature leaves, lending weight to Lubbock's (1894) statement that they 

 are throughout the genus of especial use in protecting the young leaves 

 and flowers. 



The petioles of Nymphaeas necessarily vary in length according to 

 the depth of water in which the plant grows, being always long enough 

 to allow the leaf some freedom in floating about ; the range is therefore 

 from a few centimeters to 5 or 6 meters, and that in the same species 

 (N. alba, odorata). In diameter the smallest are those of N. tetragona, 

 0.3 cm. through, and the largest are found in N. lotus, 1.9 cm. through. 

 They vary very little from a cylindrical shape, being, near the ends, 

 slightly flattened on the upper side. Of a uniform green in most species, 

 many of the cells contain a blue-purple pigment in the blue-flowering 

 species, or red-purple in the Lotos group ; N. odorata has usually deep 

 crimson-brown petioles, and in N. tuberosa they are quite characteristically 

 marked with longitudinal brown stripes in the upper part. Always 

 pubescent when young, the hairs persist only at the base in most species, 

 but are permanent in the majority of the Lotos group, and in occasional 

 specimens of N. odorata ; Caspary (1865) had such from New York State 

 on which he founded his variety villosa, and we have cultivated such a 

 plant, sent from Florida by Mr. Soar of Little River, in the Botanic 

 Garden of the University of Pennsylvania. A plentiful growth of short 

 filamentous algae on the petioles and under surfaces of leaves has been 

 mistaken for pubescence by some writers. 



Surface sections of the petiole reveal an epidermis composed of four- 

 sided cells arranged in fairly regular longitudinal rows, mostly with the 

 longest dimension lengthwise of the petiole ; the cross-walls are often 

 oblique. At intervals of 1 or 2 to 1 5 or 20 cells, the rows are interrupted 

 by circular, thick-walled cells, the bases of the hairs mentioned above. In 

 the Castalia group, hair-bases seem to be most plentiful in N. odorata, 

 though in all species they differ in number at different levels on the 

 petioles. In transverse section, the epidermal cells vary in shape from 



