TISSUES FOR SYNTHESIS 137 



. function of secretion include glandular hairs, the walls 

 of secretion cavities, individual secretion cells and 

 oil ducts. 



Glandular , Hairs. — The histological forms which 

 glandular hairs may assume have been described in 

 the section on Plant Hairs (Chapter VII). Glandular 

 hairs are outgrowths of the epidermal tissues and 

 possess glands consisting of one or more cells, which 

 have the power of secreting or producing volatile 

 oils or resins. In some instances, the gland cavities 

 are formed by a separation of a thin membrane from 

 the upper surface of a number of modified epidermal 

 cells; in others no special cavity is apparent, and the 

 secretions are evidently stored within the gland cells. 

 Glandular hairs may occur on leaves, herbaceous 

 stems and the petals of the flower. The secretions 

 include volatile oils, resins or oleoresins. 



Secretory Cavities. — Secretory cavities may occur 

 in the internal tissues of leaves, barks, roots, woods, 

 fruits and seeds. According to the manner of their 

 formation they are subdivided into schizogenous and 

 lysigenous types. Schizogenous cavities are formed 

 through enlargement of the intercellular spaces in 

 the region adjacent to the secreting cells (Plate 49, 

 No. 2). The secretory products dialyze into the 

 intercellular space and cause distention of the latter. 

 The mature schizogenous cavity appears to be com- 

 pletely surrounded by a layer of secreting cells. Lysig- 

 enous cavities result from the disintegration of a group 

 of secretory cells. This is brought about through 

 distention of the secreting cells by accumulated secre- 

 tions. The cells finally burst and discharge their 

 contents into a common cavity (Plate 49, No. 1). 



