44 



THE WATERLILIES. 



hairs. Such hairs are slender lines of terete cells, of almost even 



diameter throughout, but tapering at the apex, 



and attaining a length of 0.48 cm. in N. caerulea, 

 0.6 cm. in N. tuberosa, or i cm. to 1.3 cm. in 

 N. lotus. The basal epidermal cell is cubical 

 in shape, and if we represent its depth by 

 unity, the lengths of the succeeding cells will be 

 approximately 0.8 to 1.3, 0.5 to 2.2, 2.2 to 10, 

 and so on up to 15 or 20 times as long as broad. The relative and 



actual diameters of these hairs in differ- 

 ent species is shown in the accompany- 

 ing table. In addition to these, hairs 

 with thick multicellular base and slender 

 shaft occur in N. tuberosa and lotus. 

 The lower part of such a hair consists 

 of i to 3 tiers of polygonal cells about 

 one-third to one-half the diameter of 

 the basal column of the hair ; then 

 follow 2 to 5 short cells in linear series, 

 and finally a row of long cells as in the 

 hairs first described. These complex 

 hairs may arise from the simpler type 

 by upgrowth of the tissues supporting 

 them. Those of N. lotus are much 

 larger than of N. tuberosa ; indeed in 

 the former species the surface of the 

 stem is completely occupied by these 

 hair-protuberances. 



Much more sharply than in the root, 

 we recognize in the stem three cortical 

 regions (Figs. 16, 17, 18), an outer, 

 dense, sub-epidermal layer o. 16 to 0.3 

 cm. thick, a median spongy layer 0.6 to 

 2 cm. thick, and an inner dense layer continuous with the parenchyma which 

 makes up the central core of the stem. The spongy layer is not continuous, 

 but is cut into irregular disconnected blocks by plate-like trabecula; of dense 

 tissue passing radially from outer to inner cortex. The cells of the 

 outer cortex in N. odorata (Fig. 17) are nearly isodiametric, thin-walled, 

 and contain 6 to 8 starch grains each; there are 12 to 14 layers of 



Fio. 17. Microscopic section of rhizome of N. 

 odorata ; showing exo-cortex and 3 chains of the 

 spongy medio-cortex, e, epidermis; t, tannin 

 (latex) cell. Camera lucida sketch. 



