The Spiral Disposition of the Leaves. 531 



to a continuous screw-like l)an(l which corresponds ex- 

 actly to the leaf-spiral on the outer side. 



Twisted stems look as if they were inllated (Figs. 

 122 and 123), and are much thicker tlian the normal 

 stems of the same species. Longituchnal 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 Galiiun} It can now easily be confirmed 1)y 

 every one on the material afforded by my heritable races. - 



In Dipsacits syhesfris torsus the spiral arrangement 

 oi 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, Monatsher. d. k. Akad. d. IViss., Berlin. 1854. p 

 440- See Bof. Zcitung, 1873, p. 31 ; H. Klebahn, Ber. d. d. hot. Ges., 

 Vol. VI, p. 346. See also Ucher die Erblichkeit dcr Zivangsdrchungcn, 

 same journal, Vol. VII, p. 291. 



'For the literature of the subject see Monogvat^hic dcr Zzi'angs- 

 drchuugcn. Jahrh. f. wiss. Bot., Vol. XXIII. 1891. 



