Petiole-Pulvinus Preparations of Mimosa pudica. 215 



1. The effect of wound or section in modification of normal excitability. 



2. The change of excitability after immersion in water. 



3. Quantitative determination of the rate of decay of excitability in an 



isolated preparation. 



4. Effect of amputation of the upper half of pulvinus. 



5. Effect of removal of the lower half. 



6. Influence of the weight of leaf on rapidity of responsive fall. 



7. The action of chemical agents. 



8. Effect of " fatigue " on response. 



9. The influence of constant electric current on recovery. 



10. The action of light and darkness on excitability. 



11. Effect of desiccation and of injury on conducting tissues. 



The isolated petiole-pulvinus preparation is made by cutting out a portion 

 of the stem bearing a single lateral leaf. The four diverging sub-petioles may 

 also be cut off. In order to prevent rapid drying, the specimen has to be 

 kept in water. Preparations made in this way often appeared to have lost 

 their sensibility: I was, however, able to trace this loss to two different 

 factors : first, to the physiological depression due to injury caused by section, 

 and, second, to the sudden increase of turgor brought on by excessive absorp- 

 tion of water. I shall now proceed to show that the loss of sensibility is not 

 permanent, but is capable of restoration. 



1. Effect of Wound or Section in Modification of Normal Excitability. 



In connection with the question of effect of injury, it is to be borne in 

 mind that after each excitation the plant becomes temporarily irresponsive 

 and that the excitability is fully restored after the completion of protoplasmic 

 recovery. A cut or a section acts as a very intense stimulus, from the effect 

 of which the recovery is very slow. If the stem be cut very near the leaf, 

 the excitation of the pulvinus is very intense, and the consequent loss of 

 excitability becomes more or less persistent. But if the stem be cut at a 

 greater distance, the transmitted excitation is less intense, and the cut 

 specimen recovers its excitability within a moderate time. I have also 

 succeeded in reducing the excitatory depression by previously benumbing 

 the tissue by physiological means. The isolated specimen can be made still 

 more compact by cutting off the sub-petioles bearing the leaflets ; the 

 preparation now consists of a short length of stem of about 2 cm. and an 

 equally short length of primary petiole, the motile pulvinus being at the 

 junction of the two. 



For the restoration of sensitiveness, and to meet working conditions, the 



