Ill 



The leaf. The epidermis of the upper surface is smooth 

 and fairly thick. The lateral walls of the cells are slightly 

 undulating. The outer walls of the epidermis of the lower 

 surface are not specially developed. Stomata are confined to 

 the lower surface and have no protective devices. Hairs, of 

 one kind only, viz. peltate, occur on both sides of the leaf. 

 They agree most closely with the corresponding hairs in Rhod. 



Fig. 25. Lyonia calyculatu. 



The leaf. 3, Peltate hairs on the lower surface. Cf. note p. 81. (Finland.) 



lapponicum, but on the lower surface they do not play any 

 important part as a protective mechanism to the stomata, as 

 is the case in Rhod. lapponicum. According to LmroRSs, chloro- 

 phyll grains occur in the upper epidermis. 



The palisade-tissue, which consists of 3 — 4 layers of fairly 

 small cells, passes by easy stages into a lacunal central part, 

 formed by trabeculæ of non-branching parenchymatous cells 



