170 BOTANICAL GAZETTE [MARCH 
same structure as the horizontal; however, they are more hairy and 
the cortex contains chlorophyll and raphides. In the first year of 
growth these shoots have no thick-walled secretory cells, and although 
the leptome constitutes an uninterrupted zone, the hadrome forms 
only two arches, separated from each other by two very broad rays 
of parenchyma. The stems of Mitchella increase very little in thick- 
ness, but they are woody and persist, as stated above, for several 
years. 
' The leaf-blade.—The cuticle is not very thick, but distinct; it is 
smooth on the lower face of the blade, except below the midrib, but 
wrinkled on the upper. The structure of the epidermis is somewhat 
_ peculiar. Viewed en face the lateral cell walls are very prominently 
undulate on both faces (fig. 10); besides that, local thickenings of 
these cell walls are very conspicuous. A transverse section (jig. IT) 
shows this structure perhaps more clearly, and the thickenings are 
seen to extend from the outer cell wall to the inner as columns. 
Whether this structure be common or not, it has not been recorded 
as characteristic of any of the Rubiaceae in the work of SOLEREDER. 
It was first described and figured apparently by Mout? in the leaf 
of Helleborus foetidus, which also is an evergreen. However, it does 
not seem as if this particular structure is characteristic of plants 
with persisting leaves, since LALANNE,? who examined several genera 
of various families, does not mention any cases similar to the one 
described above. But in a paper by GopFRIN'? a somewhat analo- 
gous structure is mentioned as occurring in the cotyledons of Aesculus 
Hippocastanum and Acer platanoides; and P&r-Lasy'' records 4 
similar case from the cotyledons of Mimosa pudica; the thickenings, 
however, do not extend to the bottom of the cell in these instances, 
but only to the middle. 
The outer cell wall of the epidermis is moderately thickened on 
8 Mout, Huco von, me der Anatomie und Physiologie der vegetabilischen 
Zelle. Braunschweig. 1851. p. 14. 
9 LALANNE, Gaston, Recherches sur les caractéres anatomiques des feuilles per- 
sistantes des Wisc etisiek, esr 1890. 
10 GODFRIN, J., Recherch tomi ée des cotyléd t de l’albumen. 
Ann. Sci. Nat. Bot. VI. rg:90. 1884. : 
tt PéE-LaBy, E., Recherches sur l’anatomie comparée des cotylédons et des 
feuilles des hte. Toulouse. 1892. p. 19. 
