PROPERTIES OE THE LEAP OF DIONTEA. 
19 
With reference to the second and less important of them, I will refer to the following 
observations made in the Laboratory of the Loyal Gardens at Kew in the summer of 
1878. 
Negativity of lobe to midrib .—A leaf having been cut off and placed in the warm 
chamber, of which the temperature varied from 29° C. to 33° C. with the leaf-stalk 
in water, leading off contacts were made on the external surface of one lobe (m) and on 
the midrib /(see fig. 9). The difference"'" of potential was at first — 0’006 D. The 
leaf was then excited by touching the right central hair at intervals of 5" for 
70'. Each excitation produced a normal diphasic variation, indicating that m 
became first negative, then positive to / After each excitation the difference 
was compensated. After the first two it fell to — 0‘0026 D. and thereafter to 
— O'OOOG D. In other words, the after-effect of excitation (see Part V.) was opposed 
in direction to the original difference. A second leaf was prepared in the same way 
Fig. 9. 
Leaf led off: from under surface of right lobe and under surface of midrib, excited from left lobe. 
and left in the chamber, of which the air was nearly saturated, all night, the tempera¬ 
ture being 29° C. At 11.40 next morning the difference was —0‘004 D., having 
been — 0‘009 D. the evening before. After excitation of the hairs of the opposite 
lobe it fell to —0’0026 D., and subsequently to —0*001 D. A third leaf, similarly led 
off and placed in a chamber as before, showed a difference of —0‘0214 D., the lobes 
and marginal hairs being fully expanded. After the first mechanical excitation of the 
hairs of the opposite lobe, the marginal hairs became incurved without any further 
change of form of the leaf; the difference fell to —0*019 D. After a second excita¬ 
tion it was —0'015 D. and then sank, after repeated touches of the hairs, until, 
75 minutes after the first observation, the leaf escaped from the holder without further 
disturbance of the leading off contacts, the last reading being —0*012 D. It remained 
* To save unnecessary repetition in the following pages tbe word difference, printed in leaded type, 
will be used for “ difference of potential.” It need scarcely be added that tbe letter D. stands for Daniell. 
D 2 
