178 HISTOLOGY OF MEDICINAL PLANTS 
OIL CAVITY 
Canella alba contains an oil cavity resembling in form the 
mucilage cavity of elm bark. 
Secretion cavities occur in most of the umbelliferous fruits. 
For each fruit there is a more or less constant number of cavities. 
Anise has twenty or more, fennel usually has six cavities, and 
parsley has six cavities. 
In poison hemlock fruits there are no secretion cavities. In 
certain cases, however, the number of secretion cavities can 
be made to vary. This was proved by the author in the case 
of celery seed. He found that cultivated celery seed, from 
which stalks are grown, contains six oil cavities (Plate 122, 
Fig. 2), while wild celery seed (Plate 102, Fig. 1), grown for its 
medicinal value, always contains more than six cavities. Most 
of the wild celery seeds contain twelve cavities. 
Many leaves contain cavities for storing secreted products. — 
Such storage cavities occur in fragrant goldenrod, buchu, thyme, 
Savary, etc. 
The leaves in which such cavities occur are designated as 
pellucid-punctate leaves. Such leaves will, when held be- 
tween the eye and the source of light, exhibit numerous rounded 
translucent spots, or storage cavities. 
GLANDULAR HAIRS 
The glandular hair of peppermint (Plate 60, Fig. 3) and other 
mints consists of eight secretion cells, arranged around a central 
cavity and an outer wall which is free from the secretion cells. 
This outer wall becomes greatly distended when the secretion 
cells are active, and the space between the secretion cells and 
the wall serves as the storage place for the oil. When the mints 
are collected and dried, the oil remains in the storage cavity 
for a long time. 
STONE CELLS 
The stone cells of the different cinnamons (Plate 65, Fig. 1) 
store starch grains; these grains often completely fill the stone cells. 
The yellow stone cells of calumba root (Plate 65, Fig. 2) 
usually contain four prisms of calcium oxalate, which may be 
nearly uniform or very unequal in size. 
