The Morphology of Ruppia Maritima. 



91 



These reactions confirm Sauvageau's assertion that these cells are 

 tanniferous. As is well known, tannin is a common byproduct 

 in plants, and in this case is possibly deposited in special cells on 

 account of the difficulty of its diffusion through the epidermis. That 

 these tanniferous cells should be more abundant toward the base of 

 the leaf is natural, for it would be more economical for the plant 

 to devote as many as possible of the cells in the upper part of 

 the leaf to photosynthesis. 



(4) Absence of Stomata. 



Another peculiarity of the epidermis is the absence of stomata, 

 which will be discussed later (p. 118). 



b. Subepidermal Layer. 



Below the epidermis, at all parts of the leaf, is a distinct layer 

 one cell thick, which I have termed the subepidermal layer (PL VII, 

 fig. 43), composed of cells about twice 

 the width, tangentially, of those of the 

 epidermis ; and longitudinally, i. e. running 

 the length of the leaf, many times longer 

 than the epidermal cells (Text-fig. 13). 

 This layer contains a few chloroplasts 

 (cf. Sauvageau, 1891, II, p. 293). 

 ■ c. Vascular System. 



The vascular system of the leaf is ex- 

 tremely simple. Three strands of con- 

 ducting tissue are present — one large 

 axial and two small marginal. 



(1) Course of Vascular Bundles. 



These three vascular strands enter the 

 leaf separately at its insertion on the stem. 

 The axial bundle maintains a median po- 

 sition and extends to very near the tip 

 of the leaf (PI. VI, figs. 26, 30 ; PL VII, 

 fig. 43) ; the two lateral bundles enter 



one on each side of this axial bundle, and throughout their extent 

 run parallel to it (PL VII, fig. 43, lb). 



In the region of the sheaths each of these lateral bundles runs 

 along the edges of the leaf proper, just at its line of junction with 

 the sheaths, and above the leaf sheaths they retain this marginal 

 position. I can confirm Sauvageau's (1891, 11, p. 210) observation that 

 they do not unite with the median bundle near the apex of the 

 leaf, but disappear — according to my preparations, about 10 mm. 

 from the apex. 



Trans. Conn. Acad., Vol. XIV. 7 December, 1908. ^ 



Eigure 18. — Portion of sub- 

 epidermal layei" of leaf 

 blade, showing a few clilo- 

 roplasts. Drawn from 

 longitudinal section cut 

 from living leaf, x 335. 



