58 RESEARCHES ON IRRITABILITY OF PLANTS 



has been shown to be similar in the two cases. We may 

 next study the effect of load on the work performed. Work 

 is measured by the product of the weight raised and the 

 height of the lift. In the response of muscle, if the increas- 

 ing loads are represented by W^ Wg, Wg, and the correspond- 

 ing heights of response by h^ h^, hg, then it is found that up 

 to a certain limit W^hj < Wgh^ < Wghg ; in other words, the 

 work performed is increased under enhanced load and 

 increasing tension. 



Turning to the effect of increasing load on the response 

 of Mimosa, we find that with a load of loo mgrms. the 

 height of response is 41 ; the value of W^h^ is therefore 4100 ; 

 under a load of 500 mgrms., Wgh^ = 500 x 28 = 14,000 ; 

 and, lastly, with a load of 2000 mgrms., Wghg = 2000 X 13 

 = 26,000. It is thus seen that as in the contractile response 

 of animal, so also in that of the plant, greater amount of 

 work is performed under increased load and higher tension. 



We may now try to obtain some idea of the absolute 

 amount of work performed and the rate of work. We shall 

 take the tase where the plant had to lift a weight of 2000 

 mgrms. The following data are available from fig. 26. The 

 weight is seen to be lifted through 12 mm. in the course of 

 ten successive dots, each representing -i second. The mag- 

 nification of the lever was three times ; the absolute hft is 

 therefore 4 mm. The load to be lifted was 2000 mgrms. ; but 

 the weight of the leaf was 130 mgrms. and this helped the 

 fall. The actual work performed is therefore (2000 — 130) 

 X 4 miUimetre milligrams. This was accomplished in the 

 course of a second. Hence the absolute rate of work was 

 7480 mm. mgrms. per second. 



Effect of Temperature 



Our next inquiry is into the effect of temperature on 

 the response of the plant. For this we have to subject the 

 plant to different temperatures — some low, some high — 

 and to find means of maintaining it constant at any definite 

 temperature required. For this purpose a plant-chamber. 



