204 MR R. J. D. GRAHAM ON 



position enables full advantage to be taken of the optimum light of the early and the 

 late day. 



Tegumentary System. — The surface of the stem of the Ephedreae closely resembles 

 that of an ordinary Equisetum, in possessing longitudinal ridges and furrows (Plate I., 

 fig. 15), the former corresponding in position with hypodermal stereom strands. 

 The cells of the epidermis are rectangular or slightly hexagonal in shape, being 

 elongated in the direction of the stem axis. The cells at the base of the internode are 

 not usually so much elongated as those in the middle portion of the same. The outer 

 cell walls consist of three strata (Plate I., fig. l) ; the most external is a heavily cutinised 

 stratum, bounding a middle layer of mucilage, containing small crystals or granules of 

 calcium oxalate, which tend to have a stratified arrangement. This layer is limited 

 internally by a thick stratum of cellulose. The cells contain the normal cell con- 

 stituents, with, in some cases, starch grains, while again the cell contents may be 

 stained various shades of yellow. The coloration is apparently due to the presence of 

 tannin, as the cells give a black reaction on treatment with ferric acetate. In some 

 cases the epidermal cells are divided into two by a wall which may be parallel, or nearly 

 so, to any of the three dimensions of the cell. Either of the daughter-cells may further 

 divide by a wall inclined at an angle to the first division wall (Plate I., fig. 2). In 

 some species this division occurs more frequently in the neighbourhood of a stoma, 

 though it may also be shown in independent cells. No trace could be found of the 

 pores recorded by Stapf as passing through the cell wall. The only suggestion of their 

 appearance was the striation in the cellulose layer seen after treating the section with 

 sulphuric acid and methylene blue. These striae ended at the limit of the cellulose layer. 



The epidermal cells covering the ridges are, as a rule, larger than elsewhere ; while 

 the external walls are either markedly convex outward, or bear on their outside papillae 

 into the base of which a blunt protoplasmic protrusion extends (Plate I., fig. 3). The 

 roughness of the surface of the shoot is determined by the number of papillae (Plate I., 

 fig. 4). The core of the papilla appears to be mucilaginous, and on the addition of 

 water it swells, bursting the cuticle with which it is covered. Owing to the similarity 

 of these papillae to those found in leaves, and described by Haberlandt (l) as light- 

 sense organs, an attempt was made to test their optical properties, Graham (2). In 

 this, methods essentially those of Haberlandt were used. A piece of the young shoot 

 about 1 cm. in length was divided into two. One half was then laid upon a glass slide, 

 while the epidermis was freed from the adjacent tissues by gently scraping with a 

 scalpel. The epidermis was now mounted upside down on a cover-glass, which was 

 then used to roof a moist chamber about 4 mm. deep. The preparation was then 

 placed on the stage of a microscope, extraneous light being shut out by enclosing the 

 stage and tube in a black hood. The sub-stage iris was partly closed, when the whole 

 field appeared darkened, with the exception of certain lighted areas corresponding in 

 position with the papillae (Plate I., fig. 5). Further, the image of an object, either 

 stationary or in motion, placed before the microscope, could be clearly seen in the light 



