v Movements of Plants 93 



suggestions of Wiesner, Strasburger, Wortmann, Noll, 

 Vines, and others. 



In the last section of his Presidential address Mr. 

 Francis Darwin states his position in regard to circum- 

 nutation. He cites the most important criticism of The 

 Power of Movement, that of Wiesner, who denied that 

 circum nutation was a widespread phenomenon ; that some 

 stems, leaves, etc., grow in a perfectly straight line ; that 

 such curvatures as those of geotropism and heliotropism 

 cannot be interpreted as modifications of circumnutation. 



Yet, for reasons given, Mr. Francis Darwin confesses 

 that he "cannot give up the belief in circumnutation as a 

 widely-spread phenomenon, even though it may not be so 

 general as was supposed." He adopts Vbchting's concep- 

 tion of " rectipetality " "a regulating power leading to 

 growth in a straight line," and says, " The essence of the 

 matter is this : we know from experiments that a power 

 exists of correcting excessive unilateral growth artificially 

 produced ; is it not probable that normal growth is simi- 

 larly kept in an approximately straight line by a series of 

 aberrations and corrections? If this is so, circumnutation 

 and rectipetality would be different aspects of the same 

 thing." 



"A bicycle cannot be ridden at all unless it can 

 'wobble,' as every rider knows who has allowed his 

 wheel to run in a frozen rut. In the same way it is 

 possible that some degree of circumnutation is correlated 

 with growth, owing to the need of regular pauses in growth. 

 Rectipetality would thus be a power by which irregularities, 

 inherent in growth, are reduced to order and made sub- 

 servient to rectilinear growth. Circumnutation would be 

 the outward and visible sign of the process." 



Phases of Botany, Pre-Hellenic to Neo-Hellenic. 

 Hence, whatever detailed value be retained by the special 



