The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . s with veryrare exceptions; it is not until later that this arrangement ^ Al. Braun, Monatsher. d. k. Akad. d. IViss., Berlin. 1854. p440- 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 Zziangs-drchuugcn. Jahrh. f. wiss. Bot., Vol. XXIII. 1891. 532 Heritable Spiral Torsions. is changed into the spiral one, and in different
The mutation theory; experiments and observations on the origin of species in the vegetable kingdom . s with veryrare exceptions; it is not until later that this arrangement ^ Al. Braun, Monatsher. d. k. Akad. d. IViss., Berlin. 1854. p440- 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 Zziangs-drchuugcn. Jahrh. f. wiss. Bot., Vol. XXIII. 1891. 532 Heritable Spiral Torsions. is changed into the spiral one, and in different individualsthis occurs at varying ages. If a transverse section ofthe plant is then examined under high power, at thelevel of the growing point, the spiral arrangement of theleaves can easily be seen. Taken later, i. e., during theelongation of the stem, such transverse sections have stillmore or less the same appearance (Fig. 124 B). Theouter leaves of this figure have been cut through theirlower parts where they are fused laterally with oneanother; their left-hand spiral can easily be followed. Fig. 124. Dipsacus sylvestris torsus. A, a transverse sec-tion through a seedling a Httle above the growing pointshowing the normal decussate arrangement of theleaves; c, c, the cotyledons; B, a transverse sectionthrough the still young point of the stem of a twistedindividual with spiral arrangement of leaves. in the figure. The subsequent leaves were still veryyoung and were therefore cut across their upper freeparts, but are nevertheless obviously arranged in a three youngest leaves do not seem to form part ofthe spiral, but a trimerous whorl, such as very oftenoccurs in the upper part of the stem of twisted speci-mens of Dipsacus If the angle of divergence of theleaves is measured it usually corresponds pretty closely The Spiral Disposition of the Leaves. bi^to one of the ordinary types of leaf arrangement, (e. g., %). In the rosettes of radical leaves, where the intern
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