OF THE LEAVES OF CERTAIN SPECIES OF VERONICA. 249 
been shown that certain features are constant through whole genera or even 
orders : among these are the form of hairs and of secretions and the stomatal 
apparatus *, Several anatomical features of this kind have been noticed in 
the species examined. 
Epidermal  Cells.—A feature of the epidermis may be mentioned in this 
connexion ; in all the species examined the lateral walls of the epidermal cells 
are rectilinear or very slightly curved, not sinuous. They may be very thick 
and pitted. These features are not common to the whole genus, as the 
herbaceous forms have the epidermal cells with sinuous walls on the lower 
side of the leaf f. 
Hairs.—Asin all Scrophulariacez the hairs are uniseriatef. Two main types 
of hairs occur, glandular and eglandular ; the former are of two kinds, short- 
stalked and long-stalked, the first kind being much commoner. In the short- 
stalked hairs the stalk consists of one or two cells surmounted by an oblong 
glandular head divided into two by a vertical wall Ti$. This form of hair is 
typically abundant in the region of the axillary end, where it probably helps 
to retain and absorb moisture. Long-stalked glandular hairs occur in very 
few species f ; the stalk consists of a row of 4-6 thin-walled cells, with a small 
spherical undivided head. The eglandular hairs are never branched ; they 
are of varying form, either unicellular or consisting of a row of 2-6 cells. 
The walls of the cells are very much thickened in some cases and may be 
serrated externally in some cases f. 
In none of the species examined are hairs very numerous, but, with the 
exception of V. subalpina, all possess some hairs on the leaf. In many cases 
hairs are confined to the region of the axillary bud. 
Secretion.—As recorded by Solereder $, the only form of internal secretion 
is tannin, а feature characteristic of the whole order.  Tannin-sacs occur 
either singly or in groups in the mesophyll of all the species examined, though 
Huchedé f mentions a complete absence of secretory organs, 
Stomata.—In surface view the stomata, in common with the rest of the 
order, are surrounded by three or more epidermal cells f. In most cases the 
stomata occur on both sides, either in more or less equal numbers or in greater 
number below, but sometimes they are confined to the lower side. In no 
case are stomata confined to the upper side. 
Hydathodes.—Though not common to all the species, these may be mentioned 
here. The hydathodes in most cases where they occur are of the simple kind. 
At the tip of the leaf the vascular bundle ends in a mass of small-celled paren- 
chyma. The epidermis in this region has much thickened walls with cuticle ; 
* Cf. Fritsch (1903). + Huchedé (1907). f Solereder (1908), $ Vesque (1885). 
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