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F 
OF THE LEAVES OF CERTAIN SPECIES OF VERONICA, 295 
bo 
midrib, and short-stalked glandular hairs on the under side. V. parvifolia, 
Vahl, is very similar, but has shorter thinner leaves. Structurally these two 
species are very much alike. Both have stomata on both sides of the leaf : 
in V. parviflora there are few above and a great number below, while in 
V. parvifolia they are numerous on both sides. The mesophyll is differen- 
tiated into palisade and spongy tissues, but the latter has very few interspaces. 
V. parviflora has been compared with native-grown herbarium material, and 
the two leaves agree in all points of structure and arrangement. 
The species described above are the least xerophilous of those examined, but 
even they have certain xerophilous features in the protection of the stomata 
and the reduction of the intercellular spaces in the mesophyll. 
(корр В. 
The species included in this group are like V. parviflora, but have marked 
xerophilous adaptations ; the leaves are thick and have the epidermis much 
thickened and cuticularized. The central bundle ends in a hydathode. 
V. Pseudotraversi, Hort. Edin. 
This forms the connecting-link with Group A. The leaves are elongate, 
concave above, and glabrous except for a few glandular hairs on the lower 
surface. The stomata are slightly sunk, with cuticular expansions above. 
The mesophyll shows a slight differentiation, but less than in any of the 
preceding group. 
V. ignota, Hort. Edin. 
The leaves are narrow and thick, glabrous except for a few glandular hairs 
over the midrib. The outer epidermal wall is much thickened and cuticu- 
larized with expansions over the stomata. The mesophyll is very homogeneous 
(fig. 8) and consists of slightly elongated cells, closely packed together ; those 
at the lower side are rather smaller. Tannin is abundant. 
V. rakaiensis, Armst. 
The leaves are broader and thicker than in V. ignota, with a few glandular 
hairs scattered over the upper surface ; structurally the mesophyll shows still 
less differentiation, it is quite homogeneous, being composed of square cells 
with few intercellular spaces. Cork is developed early at the leaf-base, 
whereas in V. ignota and V. Pseudotraversi it does not appear till later. 
Group C. 
The species of this group have their leaves small, elliptic-lanceolate, and 
usually rather concave above. The texture of the leaf is rather leathery. 
