STRUCTURE. 



43 



12, 13, 14, f, 15, 1 6, 17, f, 18, 19, 20, f, 21, 22, 23, f, 24, 25, 26, f, &c; 

 the primary spiral seemed to be sometimes ^ T , sometimes higher. N. 

 rubra in the Munich garden (which Raciborski considered was more 

 probably a hybrid) showed i, 2, f, 3, 4, 5, 6, f, 7, 8, f, 9, 10, n, 12, f, 



13, 14, 15, 16, f, 17, 1 8, f, 19, 20, 21, 22, f, 23, 24, 25, 26, f, 27, 28, f, 

 29, 30, 31, 32, f, 33, 34, 35, 36, f, 37, 38, f, 39, 40, 41, 42, f, 43, 44, 



45. 46, f, 47. 48, f, 49. 50, 51- 52, f, 53- 54, 55- 56, f. 57, 58, f, 59, 60, 

 61, 62, f, &c.' 



The structure of the stem in Nymphaeaceae has long been a puzzle, 

 and for the most part still remains so. A transverse section of any 

 vegetative stem of Nymphaea (Fig. 16) shows to the unaided eye three 

 well-marked regions, viz., (i) an outer wall of dense cellular tissue, about 

 o. 16 cm. thick, consisting of epidermis and exo-cortex, (2) a medio-cortex 

 full of large lacunee or air-spaces, (3) a dense central core traversed in 

 every direction by vascular bundles. The second 

 layer is traversed by numerous trabeculae of denser 

 tissue connecting the exo-cortex with the central 

 core. The following description applies only to 

 normal vegetative stems, not to stolons or resting 

 tubers. 



Microscopically examined, a well-marked epi- 

 dermis is always present. In N. lotus and odorata 



/T7- _\ .1 -11 111 FIG. 16. Rhizome of J\T. odor- 



(rig. 17) this is an irregular layer as to the level aia - transverse section ot in- 

 of the cells on the outer and inner sides, and as 



to their size, though they are approximately cubical heavy llnes are v scul a r bun- 



' , , , . ,, , dles - Natural size, 



in shape. 1 he walls are equally thin on all sides. 



In N. flava the cells are much shallower than long or broad (about 

 2:1) and form a more even surface. With the exception of a very 

 minute area at the growing point of the stem, its whole surface is 

 covered with hairs. Where these first appear outside the naked area, 

 every epidermal cell bears one. At a short distance back of this point, 

 however, many of the epidermal cells undergo an oblique division, cutting 

 off a wedge-shaped segment with its apex at the outer surface on one 

 side of the cell, and a base nearly equal to half the base of the mother 

 cell ; the apex of the wedge widens out, and soon the new cell is cubical. 

 A single cell thus comes to intervene between two formerly contiguous 



1 Raciborski's N. flava, having no runners, but an ordinary branching rhizome as in other 

 Nymphaeas, was almost certainly N. odorata sulfitrea (*V. odorata X flava) and not the true A'. 

 (lava. His N. stellata was probably N. caerulea Sav. 



