INTRODUCTION TO PLANT HISTOLOGY 



473 



the separation of cells, through solution of the middle lamella. In this case 

 the space is usually more regular in form. Such glands are called schizo- 

 genous. The surrounding cells divide tangentially to produce a special 



upper 

 epidermis 



Hydathode 



Lower 

 epidermis 



Fig. 462. — Saxifragci sp. Transverse section through leaf 

 margin showing hydathode gland. 



layer of small cells round the internal cavity. These are the secretory cells 

 and they constitute the epithelium (Fig. 464). 



Lysigenous glands are usually more or less spherical. Many of the 



T Glar)dular sac 



Fig. 463. — Citrus liiriomim. Section through peri- 

 carp of fruit, showing large lysigenous secretory 

 sacs covered only by epidermis and containing 

 essential oil. 



perfume glands in flowers and leaves are of this type. Schizogenous glands 

 may also be spherical, but they are more often elongated into secretory sacs, 

 or even into long canals, branching and anastomosing through the whole 

 plant. This kind of gland frequently contains terpenes, or " essential oils " 

 16 A 



