SPIRAL TORSION. 
the Linnean Society,’ March 6, 1855, 
BYAl 
vol. 1, p. 370). 
The stem was distended, and hollow, and twisted on 
itself; its fibres, moreover, were ar- 
ranged in an oblique or spiral direc- 
tion; the branches or leaf-stalks, which 
usually are arranged in an opposite and 
decussate manner, were, in this case, 
disposed in a linear series, one over 
the other, following the line of cur- 
vature of the stem. When the course 
of the fibres was traced from the base 
of one of the stalks, upward around 
the stem, a spiral was found to be 
completed at the base of the second 
stalk, above that which was made 
the starting poimt. Now, if opposite 
leaves depend on the shortened con- 
dition of the internode between the 
two leaves, then, in the teazel-stem 
just described, each turn of the spiral 
would represent a lengthened inter- 
node; and, if the fibres of this speci- 
men could be untwisted, and made to 
assume the vertical direction, and, at 
the same time, the internodes were 
shortened, the result would be the 
opposition of the branches and _the 
decussation of the pairs; this expla- 
nation is borne out by the similar 
twisting which takes place so fre- 
quently in the species of Galium and 
other Rubiacee. 

Fie. 172.—Twist- 
ed stem of Dipsacus 
fullonum. 
G. Franc’ was one of the first to notice this twisting 
in Galiwm, and M. Duchartre,” in mentioning a similar 
instance, gives the following explanation of the appear- 
ance which will be found to apply to most of these cases. 
In the normal stem of Galiwm Mollugo the branches 
1 «Ephem. Nat. Cur.,’ dec. 2, ann. 1, 1683, p. 68, fig. 14. 
2 * Ann. des Scienc. Nat.,’ third series, vol. i, 1844, p. 292. 
21 
