— 257 — 



The epidermis-cells which, like the barkcells, contain chloro- 

 plasts (fig. 1, A, B, D), are in the different species rather different 

 in size: being proportionally small in the species that have one 

 stratum of cells (or more) between epidermis and the outmost 



Fig. 2. Portions of the transverse sections of the stem of several Potamogeton- 

 species. A, P. j>erfoliatus ; one of the vascular bundles of the axial cylinder. — 

 B, P. coloratus ; one of the vascular bundles of the axial cylinder. — 

 G, P. lucens; endodermis. — D, P. zosterifolius ; endodermis. — E, P. natans; 

 vascular bundle from the bark formed by a small portion of phloem surrounded 

 by bast. — b, bark; e, endodermis; m, pith; si, sieve tubes; s, bast; lg, chan- 

 nels formed by obliteration of vessels; c, the outmost stratums of cells of the 

 axial cylinder. (A—D: 240:1; E\ 300:1). ' 



lacunae of the bark, while they are large where such a stratum is 

 lacking, and where, consequently, the epidermis forms the outside 

 limit of the outer lacunae. The outer walls of the epidermis-cells 

 are rather thick and very strong. As a rule they will be co- 



