368 LECTURE XV. 



has been growing more rapidly than the anterior. Like the 

 hypocotyl, the epicotyl subsequently becomes straight, but 

 not so directly. In the first place, the plumule nutates. The 

 nutation exhibits itself in the first instance as a simple oscilla- 

 tion in one plane, the effect of which is to cause variations in 

 the angle between the pendent plumule and the straight portion 

 of the epicotyl. Thus Wortmann observed in seedlings of 

 Phaseolus multiflorus that the plumule hung down parallel to 

 the straight erect portion of the epicotyl so that the angle 

 between them (the angle of nutation) was 180: in consequence 

 of the temporary more rapid growth of the concave side the 

 angle was then diminished to 90 or less, increasing again to 

 1 80 in consequence of the subsequent more rapid growth of 

 the convex side. This simple nutation in one plane is clearly 

 manifested only so long as the epicotyl is prevented from 

 nutating in other planes by the cotyledons. When it escapes 

 from between the cotyledons the alternate more rapid growth 

 of the two longitudinal halves manifests itself in a swaying 

 movement of the pendent plumule from one side to the other 

 so that it describes a semicircle. In addition to this movement 

 of nutation, Wiesner has observed that at an early stage the 

 anterior side of the epicotyl begins to grow more rapidly 

 near its base than the corresponding portion of the posterior 

 side (epinasty), so that in this region the anterior side becomes 

 convex. The whole epicotyl then somewhat resembles an 

 elongated letter S in form, the two convex portions being 

 the regions of the more active unilateral growth separated 

 by an indifferent zone, as Wiesner terms it, in which the 

 growth of the two sides is equal. It happens not unfre- 

 quently that there are more than two curvatures in one 

 internode, and they may exist simultaneously in several in- 

 ternodes, so that the form of the whole organ is more 

 complicated. This exhibition of. irregularity of growth 

 Wiesner terms undulating nutation.. In the course of the 

 subsequent growth of the epicotyl, the lower curvature first 

 disappears in consequence of hyponasty, and then the 

 upper in consequence of epinasty, so that it becomes 

 straight. 



