316 DIONAA MUSCIPULA. Cuap. XIIL 
is transmitted in like manner in all directions through 
the cellular tissue; but that its rate is largely governed 
by the length of the cells and the direction of their 
longer axes. Thin sections of a leaf of Dionza were 
made by my son, and the cells, both those of the 
central and of the more superficial layers, were found 
much elongated, with their longer axes directed to- 
wards the midrib; and it is in this direction that the 
motor impulse must be sent with great rapidity from 
one lobe to the other, as both close simultaneously. 
The central parenchymatous cells are larger, more 
loosely attached together, and have more delicate walls 
than the more superficial cells. A thick mass of cel- 
lular tissue forms the upper surface of the midrib 
over the great central bundle of vessels. 
When the filaments were roughly touched, at the 
bases of which slits had been made, either on both 
sides or on one side, parallel to the midrib or at right 
angles to it, the two lobes, or only one, moved. In 
one of these cases, the lobe on the side which bore the 
filament that was touched moved, but in three other 
cases the opposite lobe alone moved ; so that an injury 
which was sufficient to prevent a lobe moving did not 
prevent the transmission from it of a stimulus which 
excited the opposite lobe to move. We thus also 
learn that, although normally both lobes move to- 
gether, each has the power of independent movement. 
A case, indeed, has already been given of a torpid 
leaf that had lately re-opened after catching an 
insect, of which one lobe alone moved when irritated. 
Moreover, one end of the same lobe can close and re- 
expand, independently of the other end, as was seen 
in some of the foregomg experiments. 
When the lobes, which are rather thick, close, no trace 
of wrinkling can be seen on any part of their upper 
