Ciiap. I. TWINING PLANTS. 19 



occupied by each leaf with respect to the support, 

 depends on the growth of the internodes after they 

 have become spirally wound round it. I mention this 

 on account of an observation by Palm (p. 34), who 

 states that the opposite leaves of the Hop always stand 

 in a row, exactly over one another, on the same side 

 of the supporting stick, whatever its thickness may 

 be. My sons visited a hop-field for me, and reported 

 that though they generally found the points of inser- 

 tion of the leaves standing over each other for a space 

 of two or three feet in height, yet this never occurred 

 up the whole length of the pole ; the points of insertion 

 forming, as might have been expected, an irregular 

 spire. Any irregularity in the pole entirely destroyed 

 the regularity of position of the leaves. From casual 

 inspection, it appeared to me that the opposite leaves 

 of Thunbergia alata were arranged in lines up the sticks 

 round which they had twined ; accordingly, I raised a 

 dozen plants, and gave them sticks of various thick- 

 nesses, as well as string, to twine round ; and in this 

 case one alone out of the dozen had its leaves 

 arranged in a perpendicular line : I conclude, therefore, 

 Palm's statement is not quite accurate. 



The leaves of different twining-plants are arranged 

 on the stem (before it has twined) alternately, or 

 oppositely, or in a spire. In the latter case the line of 

 insertion of the leaves and the course of the revolutions 

 coincide. This fact has been well shown by Dutrochet,* 



Comptes Eendus, 1844, torn. xix. p. 295, and Annales des Sc. Nat. 

 3rd series, Bot., torn. ii. p. 163. 



