OF THE LEAVES OF CERTAIN SPECIES OF VERONICA. 269 
beyond the cell over the aperture, forming an outside chamber or vestibule 
(fig. 16 а). In other cases the guard-cells are sunk below the general level 
of the epidermis and the cuticular expansions project from the adjacent 
epidermal cells; in extreme cases, V. Traversii, there are secondary 
expansions from the guard-cells in addition (fig. 165). This species though 
Fro. 16а. Fie. 16. 
Section of stoma of lower side of leaf Section of stoma of lower side of leaf 
of V. Hectori. x 435. of Г. Traversit. x 435, 
having the most carefully protected stomata is not one of the most xerophilous 
in other ways. In the very highly xerophilous forms, V. lycopodioides ete., 
protection is rather attained by the reduetion in the numbers of stomata than 
in such special guarding of individuals. 
Hydathodes.—In general, hydathodes are characteristic of hygrophytes : 
and so their presence in such a xerophilous group as this is of considerable 
interest. Normal hydathodes occur in the less xerophilous Groups A, В, С, 
and F, even in the more modified forms of Group В. They do not oceur in 
the other more xerophilous groups. 
V. elliptica, a seaside species, has the terminal hydathode protected by the 
great thiekening of the outer walls of the epidermis in this region and 
the reduction of the stoma. The species in Group C, V. anomala and 
V. Traversii, show also а process of reduction, not only in the size of 
the opening, which is very small, but also by reduction in the extent of the 
water-discharging tissue below. 
Water-tissue.—This occurs in a few species of Veronica. The hypodermal 
layer may be very sharply differentiated from the rest of the mesophyll, as 
in V. Lewisii, but in other cases, especially in the less xerophilous species, it 
appears to be somewhat intermediate. Thus, in V. salicifolia a layer of cells 
occurs only differentiated by form, or rather more distinct in V. elliptica *. 
* Cf. Huchedé (1907). 
