26 MINNESOTA BOTANICAL STUDIES. 



cuticle is a common sheath to the whole plant. It is depressed 

 into the crevices between the cells and is therefore wavy in sec- 

 tion. It peels off in places. It shows a different, generally 

 weaker, staining reaction from the regular cell wall. The wall 

 underneath the cuticle is thin. The cuticularized epidermis 

 probably is useful in preventing evaporation when the plant is 

 exposed between tides. The hygroscopic nature of the mucilage 

 within no doubt plays a very important part in this respect. 



The epidermal cells are densely gorged with chromatophores. 

 These are yellow, highly refracting grains of oval shape. As 

 the function of the epidermis is assimilative as well as protec- 

 tive, the question arises, may not the convex outer walls of the 

 cells aid in condensing the light that is necessary for assimila- 

 tion (Kerner)? 



The epidermal cells have the power of dividing radially and 

 periclinally, cutting off basal cells that are added to the cortex 

 and cause growth in thickness. The division in planes trans- 

 verse to the axis of the plant provides for the elongation of the 

 plant. This cambium-like nature of the epidermal cells is also 

 seen in the origination of a meristematic layer where a concep- 

 tacle is to be produced {PL XI, Fig. if), and again the grow- 

 ing point is an epidermal cell {PL X.). 



Cortex. — {PL IX., Figs, i-j, 5.) Below the epidermis are 

 six or seven rows of cells of varying size and nature, differing 

 more or less from the epidermal and pith cells, and agreeing in 

 a general way in not being greatly elongated and in having 

 a large number of chromatophores. This tissue is the cortex. 

 (The epidermis is by some writers included under this name.) 

 The cells of the cortex are arranged with considerable regu- 

 larity in vertical, radial and concentric rows. The regularity 

 of shape and size tends to diminish towards the pith. 



The row of cells immediately beneath the epidermis is com- 

 posed of the basal cutoffs from the epidermal cells. They are 

 cuboidal cells of a diameter equal to the width of the epidermal 

 cells. They, like the outer cells, are gorged with color bodies. 

 The second and third concentric rows of the cortex are, in 

 cross section, of equal diameter, but a little larger than the row 

 above. In longitudinal section it is seen that these cells are 

 generally respectively two and four times as long as the basal 

 cells of the epidermis. Some of the cells also show this larger 

 size in cross-section. These cells seem still to have the power 



