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. i), 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. i) 

 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. 



