532 
Heritable Spiral Torsions. 
is changed into the spiral one, and in different individuals 
this occurs at varying ages. If a transverse section of 
the plant is then examined under high power, at the 
level of the growing point, the spiral arrangement of the 
leaves can easily be seen. Taken later, i. e., during the 
elongation of the stem, such transverse sections have still 
more or less the same appearance (Fig. 124B). The 
outer leaves of this figure have been cut through their 
lower parts where they are fused laterally with one 
another; their left-hand spiral can easily be followed 
Fig. 124. Dipsacus syhestris tarsus. A, a transverse sec- 
tion through a seedling a little above the growing point 
showing the normal decussate arrangement of the 
leaves ; c, c , the cotyledons ; B, a transverse section 
through the still young point of the stem of a twisted 
individual with spiral arrangement of leaves. 
in the figure. The subsequent leaves were still very 
young and were therefore cut across their upper free 
parts, but are nevertheless obviously arranged in a spiral. 
The three youngest leaves do not seem to form part of 
the spiral, but a trimerous whorl, such as very often 
occurs in the upper part of the stem of twisted speci- 
mens of Dipsacus If the angle of divergence of the 
leaves is measured it usually corresponds pretty closely 
