256 DIONÆA MUSCIPULA. (Cuar, XII. 
142v of an inch, so that the two extreme dots were 75} of 
an inch apart. One of the filaments was now touched and 
the leaf closed. On again measuring the distances between 
the dots, the two next to the midrib were nearer together 
by 14y% of an inch, and the two further dots by ?j3% of an 
5 
now stood about y¢%;5 of an inch (*127 mm.) nearer together 
than before. If we suppose the whole upper surface of the 
lobe, which was 429% of an inch in breadth, to have con- 
tracted in the same proportion, the total contraction will 
have amounted to about +235 or 4p of an inch (°635 mm.): 
but whether this is sufficient to account for the slight inward 
curvature of the whole lobe, I am unable to say.* 
Finally, with respect to the movement of the leaves the 
wonderful discovery made by Dr. Burdon Sanderson} is now 
universally known ; namely that there exists a normal elec- 
trical current in the blade and footstalk; and that when the 
leaves are irritated, the current is disturbed in the same 
manner as takes place during the contraction of the muscle 
of an animal.t 
* [Batalin has discussed the me- 
chanism of closure in Dionza in his 
interesting essay in ‘Flora,’ 1877. 
He agrees in general with the state- 
ments above given, but as in the case 
of Drosera, so here he believes that 
the movements are associated with a 
small amount of actual growth. 
Marks are made on the lower or 
external surface of the leaf, and the 
distance between them is found to 
increase when the leaf closes. When 
the leaf opens the distance does not 
perfectly return to its former dimen- 
sions, and thus shows a certain 
amount of permanent growth has 
taken place. It will be seen that 
Batalin’s observations do not support 
the idea (see p. 258) that the re-open- 
ing of the leaf is due to the return of 
the outer cells to their natural size 
when the tension put on them by the 
contraction of the inner surface is re- 
moved. Munk (loc. cit.) and Pfeffer 
(‘Osmotische Untersuchungen,’ 1877, 
p- 196) have with justice called at- 
tention to the unsatisfactory nature 
of the discussion in the text on the 
mechanism of the movement. Batalin 
shows further that the ultimate 
closure of the leaf by which the two 
valves are closely pressed together is 
effected by the shortening or con- 
traction of the outer surface of the 
leaf. He records a curious fact which 
has not elsewhere been noted, namely, 
that the midrib becomes more curved 
after the closure of the leaf. Munk 
(Reichert and Du Bois-Reymond, 
‘Archiv.’ 1876, p. 121), on the other 
hand, is inclined to believe that the 
curvature of the midrib diminishes 
when the leaf closes.—F, D.] 
t ‘Proc. Royal Soc.’ vol. xxi. p. 
495; and lecture at the Royal In- 
stitution, June 5, 1874, given in 
‘Nature,’ 1874, pp. 105 and 127. 
t [Professor Sanderson’s work has 
been criticised by Professor Munk in 
Reichert and Du _ Bois-Reymond’s 
‘Archiv.’ 1876, and by Professor 
Kunkel in Sachs’ ‘Arbeiten a. d. 
bot. Institut in Wiizburg,’ Bd. ii. p. 1. 
Professor Sanderson. has continued 
