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. 124 B). 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 sylvestris torsus. A, a transverse sec- 

 tion through a seedling a Httle 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 



