LE-Vr-CLIMREViS. 



43 



here represented, the increase in diameter was not quite so great. 

 In the section of the petiole in its ordinary state (A), wc see a 



Fig. 4, 

 Solanum jasminoides. 



A 



B 



A. Section of a petiole. 



B, Section of a petiole some wccts after it had clasped a stick, as shown in 

 fig. 3, 



semilunar band of cellular tissue slightly different from that out- 

 side it, and including three closely approximate groups of dark 

 vessels. Near the upper surface of the petiole, beneath two ridges, 

 there are two other small circular groups of vessels. In the sec- 

 tion of the petiole (B) which had during several weeks clasped 

 a stick, the two upper ridges have become much less prominent, 

 and the two groups of woody vessels beneath them much in- 

 creased in diameter. The semilunar band is converted into a 

 complete ring of very hard, white, woody tissue, with lines radia- 

 ting from the centre. The three groups of vessels, which, though 

 closely approximate, Avere before distinct, are now comp)letely 

 blended together. The upper part of the new ring of woody vessels, 

 formed by the prolongation of the horns of the original semilunar 

 band, is thinner than the lower part, and is slightly different in 

 appearance from being less compact. This clasped petiole had 

 actually become tliicker than the stem close beneath ; and this was 

 chiefly due to the greater thickness of the ring of wood, which 

 presented, both in transverse and longitudinal sections, a closely 

 similar structure in the petiole and axis. The assumption by a 

 petiole of this structure is a singular morphological fact ; but it 

 is a still more singular physiological fact that so great a change 

 should have been induced by the mere act of clasping a sup- 

 . port 



FuMABiACE^. — Fumaria officinalis. — It could not have been 



* Dr. Maxwell Masters informs me that in most, or all, petioles which are 

 cylindrical, such as those hearing peltate leaves, the woody vessels form a closed 

 ring, and that the semilunar hand of vessels is confined to petioles which are 

 channelled along their upper surfaces. In accordance with this statement, it 



