'1 



PLANT CURRENTS 



13 



the months of March and May, and for the experiment now on 

 the table my favourite object has been the vigorously growing 

 shoots of a vine. But in this bleak month of May (1902) the 

 vine shoots have not yet appeared, and I have therefore taken 

 a less favourable object, viz., the petioles of ivy-leaves, which, in 

 comparison with young vine shoots, must be looked upon as 

 rather a sluggish variety of vegetable tissue. So I shall take a 

 stronger mechanical stimulus than usual. 



The petiole of an ivy-leaf is fastened by modelling wax to a 

 glass plate ; to two points, 5 cm. distant from each other, un- 

 polarisable electrodes are connected, and attached, of course, by 



FlG. 4. "Plant-guillotine" for the demonstration of the mechanical 

 excitability of vegetable protoplasm. The shutter, visible only on one side 

 B, by which the twig or shoot is excited, is represented as having dropped. 



v/ires to the galvanometer. Two slips of wood (weighing 5 

 grams each) running in vertical grooves, are suspended by catches 

 i cm. above the petiole close to the electrodes, which we will 

 call A and B. I let go the slip B, which strikes the petiole near 

 the B end with an energy of 5 c.g.m.m., the spot flies off scale to 

 your right. (I readjust the spot, and when it is steady, let go 

 the slip A, and now the spot flies off to your left.) I test for 

 direction as described above, by touching the galvanometer 

 terminals with a bit of zinc wire, and seeing that by touching B 

 the spot goes to right (and by touching A it goes to left). I 

 know that when the petiole was excited at B there was current 



