111 
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 calyculata. 
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 Livrorss, 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 trabecule of non-branching parenchymatous cells 
