130 



BOTANY. 



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

 fills up the canal. 



In the ConiferaB the turpentine canals have essentially the 

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

 they occusionally unite with one another, or change their 

 direction through some of the medullary rays, the cells of 

 which hare apparently become transformed int(3 resin-secret- 

 ing tissue. 



163. — Allied to the foregoing, although formed in a 

 slightly different way, are the small secretion reservoirs of 

 many plants, and in which oils, rtsiiiis, gums, and other 



Fig 115 —Transverse sections of young stem of Ivy (Bedera Ttelix). A, young u 

 tercellular gum canal, surrounded by four cells ; c. cambium ; wb, soft bast ; B, 

 fully developed canal, g ; 6, bast ; rp, cortical parenchyma. X 800.— After Sachs. 



odorous substances are collected. The fragrance of many 

 fruits— e.^., 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, 

 Pig. 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 



