66 MICHIGAN ACADEMY OF SCIENCE. 



From the character of the curve, it would seem that internal forces, 

 including rarying turgidity, together with geotropism and heliotropism, 

 are the causes of the circumnutation. 



From the facts that plants must attain a certain age and be well es- 

 tablished in a rich bed of earth, also that a stout shoot is sent out and 

 grows Aertically for several feet before lateral off-shoots develop, the 

 conclusion might be drawn that climbing depends on the vigor of the 

 plant and that a shoot is destined from its bud-stage to be a twiner. 



To sum up the different points: 



1. The directive agents of dorsi-ventral members are light and 

 gravity; heliotropic precedes diageotropic response. 



2. Branches in their actively growing periods are sensitive to the 

 same stimuli as stems, but in a less degree. 



3. There is no morphological ujjper and lower side which is perma- 

 nent. 



4. Twining occurs as a result of circumnutation and depends on the 

 general vigor of the plant. 



