74 LEAF-CLIMBERS. Chap. II. 



can hardly be removed from its support. On com- 

 paring a thin transverse slice of such a petiole with one 

 from an older leaf growing close beneath, which had not 

 clasped anything, its diameter was found to be fully 

 doubled, and its structure greatly changed. In two 

 other petioles similarly compared, and here represented, 

 the increase in diameter was not quite so great. In 

 the section of the petiole in its ordinary state (A), 

 we see a semilunar band of cellular tissue (not 



Fig. 4. 

 Solanum jasmwoidet. 



A. Section of a petiole in its ordinary state. 



B. Section of a petiole some weeks after It bad claspt-d a stick, as shown in fig 3. 



well shown in the woodcut) differing slightly in 

 appearance from that outside it, and including three 

 closely approximate groups of dark vessels. Near 

 the upper surface of the petiole, beneath two exterior 

 ridges, there are two other small circular groups of 

 vessels. In the section of the petiole (B) which had 

 clasped during several weeks a stick, the two exterior 

 ridges have become much less prominent, and the two 

 groups of woody vessels beneath them much increased 

 in diameter. The semilunar band has been converted 

 into a complete ring of very hard, white, woody 



