130 



BOTANY. 



cells secrete a peculiar sap or gum, which passes into and 

 fills up the canal. 



In the Coniferae the turpentine canals have essentially the 

 same structure. They are found in the bark, wood and pith ; 

 they occasionally unite with one another, or change their 

 direction through some of the medullary rays, the cells of 

 which have apparently become transformed into resin-secret- 

 ing tissue. 



163. Allied to the foregoing, although formed in a 

 slightly different way, are the small secretion reservoirs of 

 many plants, 1 and in which oils, resins, gums, and other 





Fig. 115. Transverse sections of young stem of Ivy (Hedera helix}. A, young in- 

 srcellular gum canal, surrounded by four cells ; e. cambium ; wb, soft bast ; E, 

 illy developed canal, g ; b, bast ; rp, cortical parenchyma. X 800. After Sachs. 



tercellula: 



fully developed canal 



odorous substances are collected. The fragrance of many 

 fruits e.g., oranges and lemons is due to the oils and other 

 matters contained in such receptacles. In Dictamnus frax- 

 inella these are developed as follows : two mother-cells (p, p, 

 Fig. 116) appear in the hypoderma and divide by several 

 partitions, forming a mass of thin-walled secreting cells 

 (Fig. 116, B] ; these, by a degeneration of their walls, fuse 

 into a common cavity filled with oil and watery matter (Fig. 

 116, C). It appears that the outer layer of secreting cells 

 (c, c) is developed from the epidermis (Fig. 116, A, d, c); 

 hence this is partly an epidermal structure. 



Of like nature are the reservoirs in the " glandular hairs " 

 of the same plant ; in fact, the two structures are apparently 



