The Spiral Disposition of the Leaves. 531 
to a continuous screw-like band which corresponds ex- 
actly to the leaf-spiral on the outer side. 
Twisted stems look as if they were inflated (Figs. 
122 and 123), and are much thicker than the normal 
stems of the same species. Longitudinal growth has, 
so to speak, been changed into a tangential growth, as 
the course of the otherwise vertical ribs clearly shows 
in our figures. The longer the particular internodes on 
the normal individuals are, the broader are the correspond- 
ing parts on the twisted ones. In this way the funnel 
shape of the twisted Valerian, as well as other specific 
and local differences, are easily explained. 
From this we see that a right-hand torsion of the 
stem (mounting in the direction of the movement of the 
hands of a clock) must be associated with a left-hand 
leaf-spiral and vice versa (Fig. 123). 
The explanation here given was first suggested by 
BRAUN, and later demonstrated by KLEBAHN, by the 
microscopical examination of the top of the stem of a 
twisted Galium. 1 It can now easily be confirmed by 
every one on the material afforded by my heritable races. 2 
In Dipsacus sylvestris torsns the spiral arrangement 
of the leaves can be detected towards the end of the first 
summer in the heart of the rosette of radical leaves, with 
the naked eye, and without any damage to the plant. 
After germination and in the earlier stages the leaves 
are decussate (Fig. 124 A) in all the plants with very 
rare exceptions ; it is not until later that this arrangement 
*AL. BRAUN, Monatsber. d. k. Akad. d. Wiss., Berlin, 1854, p 
440. See Bot. Zeitung, 1873, p. 31 ; H. KLEBAHN, Ber. d. d. hot. Ges., 
Vol. VI, p. 346. See also Ueber die Erblichkeit der Zivangsdrehungen, 
same journal, Vol. VII, p. 291. 
2 For the literature of the subject see Monographic dcr Zwangs- 
drehungen, Jahrb. f. wiss. Bot., Vol. XXIII, 1891. 
