36 



axis, and on the lower surface of the leaves. They are absent 

 altogether on the upper leaf surface, and also on the lower sur- 

 face within a narrow zone bounded by the leaf margin and the 

 anastomosing curves of the marginal veins ; most likely, in order 

 not to obstruct the water-pores situated there. The cells bearing 

 the hairs are smaller than the surrounding epidermis cells, and 

 usually wider toward the surface. In the stem and petiole they 

 are nearly square, and each is wedged In between four of the 

 elongated epidermis cells, while on the leaf their cross-section 

 parallel to the surface is nearly circular, and each is bounded by 

 from 5 to 8 of the surrounding wavy cells. Each hair has a very 

 short pedicel, formed of two flat and low circular cells (Figs. lO- 

 14). In one single case I observed a pedicel consisting of three 

 cells. In the much thickened outer wall of the epidermis cell 

 there is a wide canal tapering toward the first pedicel cell, so that 

 the latter is separated from the former only by a small, thin, 

 circular septum. The walls separating the pedicel cells are very 

 finely perforated membranes, resembling the plates of sieve-tubes. 

 The vertical walls of both flat cells are cutinized : chloriodide of 

 zinc will show this very plainly. Concentrated sulphuric acid 

 will dissolve the cellulose elements and leave the cutinized 

 portions of these walls as well defined rings on the cuticle of the 

 epidermis of which they are a continuation. 



The hairs themselves are all unicellular, but vary very much in 

 size and shape (Figures on Plate Ixxviii). Their most common 

 form is that of a slender cylinder with a tapering blunt end, and 

 their ordinary length is from .1 to .2 mm., the width uniformly 

 about .04 mm. On young, growing parts, especially, we find 

 very slender, thinner hairs, that are often as long as one millime- 

 ter. The typical form of the hairs is very often greatly modified ; 

 some are club-shaped, globular, scythe or sickle- shaped ; many 

 divide, either directly at the base, or more frequently above, 

 into two equal or unequal branches; others again, particularly 

 on the leaf-blade, expand horizontally in the upper portion, 

 either to the right or left, with or without a stalk — In the 

 latter case the hair assuming the shape of a T. By these differ- 

 ently shaped hairs, the mucilage peculiar to Brasenia is pro- 

 duced* Wq cannot fail to discover, especially on the younger 



