Cuap. L. TWINING PLANTS. 19 
occupied by each leaf with respect to the support, 
depends on the growth of the imternodes 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 ina 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 ina 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 Rendus, 1844, tom. xix. p. 295, and Annales des Sc. Nat. 
8rd series, Bot., tom. ii. p. 163. 
