324 
F. Summers. 
Externally they appear as large black caps covering the tips of the 
teeth. In sections taken parallel to the plane of the leaf their 
peculiar structure can he well made out. They are irregular in 
shape, being composed of a mass of latex which has hardened on 
exposure to the atmosphere. In this mass are embedded the 
remains of the hypodermal and epidermal layers, ruptured when the 
latex exudes in the first period of activity of the glands. A vascular 
bundle traverses each glandular structure, terminating in a few 
groups of large spiral tracheids (Fig. 25). Into the base of the 
Fig. 25. Section through a leaf-tooth, parallel to the plane of the leaf, 
m., hardened mass of secretion ; tr. terminal tracheids. 
structure the secretion is poured, the secretory elements being in 
intimate association with the vascular nundles. 
Calcium oxalate is present in the cells of the bast and 
phyll, in the form of single or aggregated crystals. 
meso- 
