PROPERTIES OF THE LEAF OF DIOMA. 
43 
deflection was observed. (2) When the derived current was doubled (2 feet of wire) 
the after effect was always positive, whatever was the direction of the current. In 
other words, the effect showed itself in either case as an augmentation of the previous 
difference. Consequently the downwards current left behind it as its after effect, a 
current in the same direction as itself. By increasing the current, this effect, whether 
its direction is upwards or downwards, could be increased in about the same proportion. 
When the experiment was made in a leaf of which the opposite lobe was led off to 
the electrometer, no effect was observed during or after the passage of the current, 
showing that the effect was not propagated, that is, was not an excitatory effect and 
did not cause one. When similar currents were led in a similar way through the leaf 
stalk by electrodes on opposite surfaces, a polarization took place, but no effect re¬ 
sembling the one described was observable. (3) When (1) and (2) were alternated, 
that is when the current was passed through the leaf a number of times in succession 
in the same direction, but alternately with different strengths of current (1 foot and 
2 feet of wire), the effect was, of course, alternately positive (with the stronger 
current) and negative (with the weaker). In both cases the effect was evanescent, 
and the previous difference was unaffected. (4) When the length of wire was in¬ 
creased to about 5 feet (a current five times as great as in (1)), different lengths, 
however, being required in different leaves, the effect was that of an excitation, that 
is, there was a negative deflection which was cut short by a larger one in the 
opposite direction. When this was compared with that of a mechanical excitation 
of one of the hairs of the opposite lobe the two variations, although resembling each 
other, were not identical. For if in a succession of observations a momentary (tenth 
of a second) closure of a downward current of sufficient strength to excite the leaf 
was alternated with mechanical excitation of a hair of the opposite lobe so as to 
compare the effects, it was found that in the variation which followed the electrical 
excitation, the first phase w T as smaller, the second phase larger than in those produced 
mechanically. 
1st series .... 
2nd series .... 
3rd series .... 
Mechanical. 
Electrical. 
Previous difference. 
Variation. 
Variation. 
+ 0-0003 
+ 0-0028 
+ 0-0035 
- 36 +192 
- 67 +132 
-102 +110 
— 3 + off scale (i.e., over 600) 
— 10 + ditto 
-11 +500 
Each series consisted of six mechanical and as many electrical excitations. The 
mean results of each series are given in the columns headed “ Variation.” 
(5) The excitatory effect produced in (4) was followed by an “ after effect ” which 
subsided very gradually in the ordinary way, leaving behind it a lasting increase of the 
previous cross difference, and when a leaf was subjected to successive excitations, the 
Gr 2 
