SECRETION IN THE HYPERICACEZE. 459 
of the petal. In the thick part there are many passages arranged 
parallel to its long axis, most of which are seen in transverse 
sections to be near the surface exterior in the unexpanded flower. 
Some are near the other surface, while the middle of the tissue is 
nearly free from them. In the centre of the petal, where the 
tissue is becoming thinner, the passages are less numerous and lie 
almost in the centre of the mesophyll, but shghtly nearer the 
underside. At a certain distance from the thick edge only one 
row of passages is formed, and at this part of the petal the cuti- 
eularization of the epidermis becomes indistinguishable. From 
the thinnest part of the petal, where the structure is that of 
ordinary soft petals, the passages are altogether absent. In the 
petals of H. perforatum a fèw passages run up for some little 
distance from the base. They can be seen best in petals of buds 
taken a little while before the flower expands. In the mature 
petals of this species the cavity of the passage seems to have been 
obliterated. 
The glands or reservoirs of ethereal oil in some respects re- 
semble pretty closely these resin-passages, but differ in form and 
in the nature of their contents. They are present apparently in 
all the species ; but they are of very different dimensions, being 
largest in H. balearicum, of medium size in H. perforatum and H. 
calycinum, and small in H. Androsemum. The most remarkable of 
them perhaps are those of H. balearicum, which, instead of being 
sunk in the tissue as in most species, project with their covering 
of cells in the form of warts on both stem and leaf. In the 
thick-leaved species they do not affect the condition of the cells 
of the epidermis; but in H. perforatum, H. tetrapterum, &c., in 
which they abut on this tissue, the epidermal cells immediately 
over the glands are much smaller than the normal ones (fig. 12). 
They arise in the same manner as do the resin-passages, and at 
about the same time in the differentiation of the leaf, i. e. at about 
the time of appearance of the young procambium bundles. A 
mass of cells is soon distinguishable, which from the first is in eon- 
tact with the epidermis. It appears in the thin-leaved species 
before the mesophyll of the leaf has become differentiated into 
palisade and spongy tissues (figs. 10 & 11) In the thicker- 
leaved ones such differentiation can at this time be observed, 
and the gland is seen to encroach most upon the palisade-paren- 
chyma (fig. 13). The glands increase in number as the leaf 
develops, fresh ones being continually formed in the region of 
