OF THE LEAVES OF CERTAIN SPECIES OF VERONICA. 251 
bundle. Butin some cases (fig. 2) the tissue is much less in quantity and 
appears as an inclined plane. In transverse section the appearance is that of 
a horseshoe-shaped patch in the cortex (fig. 4). "This tissue arises by the 
activity of a phellogen layer that appears in this region. The divisions of the 
phellogen cut off cork-cells above, so that the development is basipetal (fig. 3). 
The phellogen ceases to divide after a short period. The time of the first 
Fic. 3, Ес. 4. 
Longitudinal radial section of part Transverse section at node of V. Coleniso, showing 
of leaf-base of V. carnosula, position of cork-cells (c). x 50. 
showing phellogen (p), cork- 
cells (c), epidermis (e), and cortex 
of stem (8). 
appearance of tbis tissue varies, but in most cases, when cork is developed at 
all, it is during the first year, while the leaf itself persists for two to three 
years. In many cases this tissue is not represented till periderm formation 
starts under the epidermis of the stem. In such cases the phellogen forming 
the cork of the leaf-base is continuous with that of the stem. In other cases, 
however, the appearance is much earlier, an extreme case being V. subalpina, 
where the tissue can be recognized in the 6th to the 8th pair of leaves 
counting from the apex. 
This arrangement of corky cells at the leaf-base stands in opposition to the 
view that the translocation of carbohydrate material is carried on in the 
cortical regions of the petiole as suggested by Haberlandt * апа Schimper f. 
The cortex being completely cut off by these cells, translocation can only go 
on in the bundle. А condition similar to that existing at the leaf-base in 
Veronica has been described by Strasburger } in Æsculus Hippocastanum, 
where a similar cork-layer is formed across the leaf-base some months before 
the leaf-fall. In Veronica it is found a year or more before the fall. 
* Haberlandt (1882 & 1909). T Schimper (1885). + Strasburger (1891, p. 487). 
