RETEST ena antag AR ~ 
Cuar. XIIL] 
RE-EXPANSION. ZFT 
The Re-expansion of the Leaves.-—This is effected at an in- 
sensibly slow rate, whether or not any object is enclosed.* 
to work at the subject, and has given 
his results in an elaborate paper in 
‘Phil. Transactions,’ 1882. It will 
be sufficient to note his conclusions 
with regard to the two points men- 
tioned in the text.. First, for the 
electrical condition of the leaf at rest. 
Sanderson rejects Munk’s method of 
cxplaining the state of the leaf by a 
mechanical schema—an arrangement 
of copper and zine cylinders. He does 
so, not only because he accepts “as 
fundamental the doctrine that what- 
ever physiological properties the leaf 
possesses, it possesses by virtue of its 
being a system of living cells;” but 
also because the facts of the case are 
not in accordance with Professor 
Munk’s theoretical deductions. He in- 
clines to admit that the electrical 
differences observed between different 
parts of the unexcited leaf may be 
partly explained by the migration of 
water. “ For on the one hand we know 
that in consequence of the surface 
evaporation, migration of water cer- 
tainly exists, while on the other we 
have proof in the experiments of Dr. 
Kunkel that such migration cannot 
occur without producing electrical 
differences.” In a similar way he is in- 
clined to believe that the gradual elec- 
trical change resulting from repeated 
excitation, as well as the after effect-of 
a single excitation, are to be explained 
by migration of water accompanying 
the motion of the leaf. On the other 
hand he believes that the primary, 
and rapidly propagated electrical 
disturbance which is the immediate 
effect of excitation cannot be due to 
water-migration, but that it is the 
expression of molecular changes in 
the protoplasm of the leaf. Prof. 
Sanderson takes occasion to correct 
the impression produced by certain 
expressions in his lecture at the Royal 
Institution in 1874. Prof. Munk, 
among others, seems to have believed 
that Professor Sanderson claimed 
absolute identity between muscular 
action and the movement of the leaf 
of Dionza. It need hardly be stated 
that no such implication was intended 
by Prof. Sanderson; the view which 
he held in 1874 he still adheres to, 
namely, that the rapidly propagated 
molecular change in an excited Dionga © 
leaf can only be identified with the 
corresponding process in the excitable 
tissues of animals. 
Certain unpublished researches 
made during the last two years have 
led Professor Sanderson to extend his 
views in the direction above indicated, 
and to conclude that the “ leaf- 
current,” i.e. the electrical difference 
between the upper and lower surfaces 
of the leaf, is intimately} connected 
with the physiological conditions of 
that part of the upper surface from 
which spring the sensitive filaments : 
thus it will probably be established 
that the “leaf-current ” and the ex- 
citatory disturbance are different 
manifestations of the same property. 
From measurements made with his 
Rheotome, of six carefully chosen 
leaves, taken from vigorous plants 
(Aug. 1887), Professor Sanderson 
found that the electrical disturbance 
produced in one lobe by stimulation 
of the other by an induction current, 
begins in the course of the second 
tenth of a second following the ex- 
citation. In five out of the six leaves 
no effect was perceptible during the 
first tenth. If we assume that the 
distance travelled by the disturbance 
is one centimeter, this gives 100 
millimeters per second as the rate of 
propagation. This, as Professor San- 
derson has pointed out, happens to be 
just about the rate of propagation of 
the excitatory electrical disturbance 
in the muscular tissue of the heart of 
the frog.—F. D.] 
* Nuttall, in his ‘Gen. American 
S 
