362 On Divergence as the Cause of Motion in Plants, 



It will, no doubt, immediately occur to the reader, that to 

 substantiate the above inference it is incumbent on me to 

 show, that removal or destruction of the upper segment is 

 followed by loss or diminution of the power of curving up- 

 wards. Now although, on account of the facility with which 

 new matter (probably endowed with moving fibres) is added 

 to mutilated plants, it be very difficult entirely to prevent 

 stems curving upwards by removal of the upper segment, yet 

 I have occasionally seen the experiment succeed, and I can 

 confidently affirm, that the process, if not prevented, is much 

 retarded, and of this fact the experiments above described 

 are a sufficient proof. In Exp. 3. the part of the stem of 

 Spearmint from which the upper segment had been removed 

 had not curved upwards at the end of three days, and in 

 Exp. 4. this action did not begin until five days after. In 

 the natural state this would certainly have occurred in about 

 twenty-four hours. 



We conclude, then, £hat as in the first series of experiments 

 the cause of motion was traced into the upper segment of a 

 divided stem, so we here find that removal of this part prevents 

 or retards the same motion. 



The experiments on the effects of notching curiously con- 

 firm and illustrate the inferences drawn from the preceding 

 experiments. 



By the process of notching, we artificially weaken the 

 contractility of one side, and enable that of the other to exert 

 itself so as to arch the stem. In this way curvature or mo- 

 tion in almost any direction may be produced at will, as in 

 Exp. 5. Exp. 6. shows the effect of notching in delaying the 

 motion upwards ; one stem notched on the upper side was still 

 horizontal on the second day after the operation. 



In Exp. 7. the process of notching has so completely de- 

 stroyed the action of the upper portion of the stem, that at 

 the end of twelve days the stem was still inclined downwards, 

 and even the apex was not turned upwards. 



If anything more be necessary to establish the fact that 

 divergence is the cause of the motion in plants here treated 

 of, it is to show that the want of this property is attended 

 with the want of the power of motion. And this I think is 

 clearly made out by the facts stated in section IV. 



I have thus endeavoured to trace a certain kind of vegeta- 

 ble motion to that property which I have termed divergence, 

 the analogy of which to irritability or contractility I have la- 

 boured to prove, 1st, by its supposed vital nature; 2ndly, by 

 its being sensible to stimulants ; and 3rdly, by its being the 

 cause of vital motion. 



Shrewsbury, July 18, 1835. Henry JOHNSON. 



