650 Mutations 



to one another than would correspond to the 

 original proportion of 5 turns for 13 leaves. 

 In fact, 10 or even 13 leaves may not rarely 

 be counted on a single turn. Or the twist 

 may become so strong locally as to change the 

 spiral into .a longitudinal line. On this line 

 all inserted leaves extend themselves in the 

 same direction, resembling an extended flag. 



The spiral on the stem is simply the continua- 

 tion of the spiral line from within the rosettes 

 of the first year. Accordingly it is seen to be- 

 come gradually less steep at the base. For this 

 reason it must be one and the same with this 

 line, and in extreme youth it must have pro- 

 duced its leaves at the same mutual distances as 

 this line. Transverse sections of the growing 

 summits of the stems support this conclusion. 



From these several facts we may infer that 

 the steepness of the spiral line increases on the 

 stem, as it is gradually changed into a screw. 

 Originally 5 turns were needed for 13 leaves, 

 but this number diminishes and 4 or 3 or even 2 

 turns mav take the same number of foliar 

 organs, until the screw itself is changed into a 

 straight line. 



This change consists in an unwinding of the 

 whole spiral, and in order to effect this the stem 

 must become wound up in the opposite direc- 

 tion. The winding of the foliar screw must 



