1907] HOLM—RUELILIA AND DIANTHERA 325 
(2. c.) have extended his observation to a large number of species of 
various sections of the genus. One of the results of their investiga- 
tion is that a complete accordance exists between the external and 
internal structure of these species of Primula. These authors pro- 
posed the reestablishment of TouRNEFoRT’s genera Primula and 
Auricula, the former characterized by possessing a monostelic, the 
latter a polystelic, axis. Whether this same peculiarity in the stem 
structure, which I have found in Dianthera americana, D. crassi- 
jolia, and D. lanceolata, may be used in classifying the species under 
two distinct genera, I must leave to future investigators to decide, who 
have access to more abundant material. 
THE LEAF 
The narrowly lanceolate and almost sessile leaves are held in a 
vertical position above the water; they are smooth and glabrous on 
both faces, while along the margins unicellular, short, pointed hairs 
occur; over these hairs the cuticle is granulous, but smooth and thin 
above the epidermis of both faces of the blade. There are only a 
very few of these hairs, and they were observed only on young leaves. 
The leaf is neither exactly dorsiventral nor unilateral, when the 
distribution of stomata and the structure of the chlorenchyma are 
considered; the stomata are just as frequent on the ventral as on the 
dorsal face, and some palisade cells occur here and there inside the 
dorsal epidermis. Viewed en face the cuticle shows no striations, and 
the lateral cell walls of the epidermis are somewhat undulate on the 
dorsal face, but almost straight on the ventral; small glandular hairs 
(fig. Io) occur on both faces of the blade. The stomata are not 
arranged in any way so as to be parallel with the longitudinal axis of 
the leaf; and they have two subsidiary cells vertical on the stoma. 
Fig. 12 shows the commonest form of the outline of the subsidiary 
cells, which seems to be less regular and more variable on the upper 
face of the leaf than on the lower. Viewed in transverse section, the 
outer wall of the epidermis is slightly thickened, and the lumen of the 
cells is wider on the upper face; the stomata are raised a little above 
the adjoining epidermis, and have a deep and wide air-chamber. In 
the lateral parts of the blade, which are much thinner than the 
median with its broad and thick midrib, the chlorenchyma (jig. 22) 
