. Carnegie Institution of Washington publication. 44 THE WATERLILIES. hairs. Such hairs are slender lines of terete cells, of almost even diameter throughout, but tapering at the apex, Species. Diameter of hairs at apex of stem. N. caerulea mm. N. tuberosa mm. N. lotus mm. N. flava mm. N. odorata mm. and attaining a length of cm. in N. caerulea, cm. in N. tuberosa, or i cm. to 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 approx
. Carnegie Institution of Washington publication. 44 THE WATERLILIES. hairs. Such hairs are slender lines of terete cells, of almost even diameter throughout, but tapering at the apex, Species. Diameter of hairs at apex of stem. N. caerulea mm. N. tuberosa mm. N. lotus mm. N. flava mm. N. odorata mm. and attaining a length of cm. in N. caerulea, cm. in N. tuberosa, or i cm. to 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 to , to , 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 cm. thick, a median spongy layer 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
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