358 Dr. H. Johnson on Divergence as the 



I. Effects of dividing a Stem which has undergone Curvature. 



Exp. 1. — A Jerusalem Artichoke (Helianthus tuberosus) was 

 tied down horizontally to a stick. In twenty-four hours the 

 stem had curved, so that its head was directed perpendicularly 

 upwards. The stem was then divided at right angles to the 

 direction of the curvature. The annexed sketch (fig. 1.), a 

 faithful copy of one traced p. 



from the plant itself, repre- l &' 



sents the appearances be- 

 fore and after division. The 

 letters a, b, c mark the cur- 

 ved stem previously to divi- 

 sion ; d 9 d the upper, e, e 

 the under or outer, segment 

 after division. The former 

 has become more, and the 

 latter less, curved than the Helianthus tuberosus. 



original stem. 



Exp. 2. — Another stem of the same plant was tied down as 

 in the above experiment. In fifteen hours it had made a neat 

 and obvious curve upwards. It was cut down, and the ex- 

 tremity and curved part were found strongly divergent on di- 

 vision. The upper segment became still more arched than 

 before, whilst the lower lost its curvature and became almost 

 straight. 



II. Effects of removal of upper Segment. 



Exp. 3. — A healthy stem of Spearmint (Mentha viridis) 

 growing very erect, was carefully pegged down in a horizontal 

 position. I then cut away the upper side for about the space 

 of one inch and a half. The lower segment immediately 

 hung down almost vertically. At the end of three days this 

 plant died, the mutilated part not having at all curved up- 

 wards ; but the uninjured part of the stem below had arched 

 irregularly so as partly to erect the stem. 



Exp. 4. — Two healthy stems were divided down the middle 

 to the distance of some inches. By means of pegs they were 

 firmly fixed down on the ground, the upper segment having 

 been removed in each. They did not begin to turn upwards 

 until five days after. 



III. Effects of Notching. 



Exp. 5. — Two Jerusalem Artichokes, nearly of the same 

 size, were secured, in the same inclined position, each to a 

 separate stick fixed in the ground. The one was then notched 



