204 DROSERA ROTUNDIFOLIA. (Cuar. X. 
the motor impulse is not transmitted by the fibro-vascular 
bundles, is plainly confirmed; and Professor Cohn has come 
to the same conclusion with respect to Aldrovanda—both 
members of the Droseraceæ.* 
As the motor impulse is not transmitted along the vessels, 
there remains for its passage only the cellular tissue; and 
the structure of this tissue explains to a certain extent how 
it travels so quickly down the long exterior tentacles, and 
much more slowly across the blade of the leaf. We shall 
also see why it crosses the blade more quickly in a longi- 
tudinal than in a transverse direction; though with time it 
can pass in any direction. We know that the same stimulus 
causes movement of the tentacles and aggregation of the 
protoplasm, and that both influences originate in and proceed 
from the glands within the same brief space of time. It 
seems therefore probable that the motor impulse consists of 
the first commencement of a molecular change in the pro- 
toplasm, which, when well developed, is plainly visible, and 
has been designated aggregation ; but to this subject I shall 
return. We further know that in the transmission of the 
aggregating process the chief delay is caused by the passage 
of the transverse cell-walls; for as the aggregation travels 
down the tentacles, the contents of each successive cell seem 
almost to flash into a cloudy mass. We may therefore infer 
that the motor impulse is in like manner delayed chiefly by 
passing through the cell-walls. 
* [Batalin (‘ Flora, 1877) experi- 
mented on the transmission of the 
of Masdevallia muscosa the impulse 
travels in a sheath of thin walled 
motor impulse, and confirms the ob- 
servations of Ziegler (‘Comptes ren- 
dus,’ 1874), from which that natu- 
ralist concluded that the vascular 
bundles form the path for the trans- 
mission of the impulse. Batalin 
concludes that impulse travels with 
far greater ease along the vessels than 
across the parenchyma, and that the 
course of the stimulus is normally 
almost exclusively along the vessels. 
If we believe that the motor im- 
pulse travels as a molecular change 
in the protoplasm, we cannot suppose 
that it travels in the tracheids. Now 
Oliver (‘Annals of Botany,’ Feb. 
1888) has suggested that in the case 
parenchyma accompanying the xylem. 
If we make a similar assumption for 
Drosera, we should get rid of a difti- 
culty, for whether the impulse 
travels in the course of the vascular 
bundles or transversely across the 
leaf, it would in either case. be 
travelling in parenchymatous tissue ; 
the only difference between the two 
cases being that the parenchyma 
accompanying the vessels would be 
specially adapted for rapid transmis- 
sion in a definite direction, whereas 
the ordinary parenchyma has to 
transmit the impulse in a variety 
of directions.—F. D.] 
