252 DROSERA ROTUNDIFOLIA. Ouar. X 
the blade more quickly in a longitudinal 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 protoplasm, which, when 
well developed, is plainly visible, and has been desig- 
nated aggregation ; but to this subject I shall return. 
We farther know that in the transmission of the aggre- 
gating 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 suc- 
cessive 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. 
The greater celerity with which the impulse is 
transmitted down the long exterior tentacles than 
across the disc may be largely attributed to its being 
closely confined within the narrow pedicel, instead 
of radiating forth on all sides as on the disc. But 
besides this confinement, the exterior cells of the ten- 
tacles are fully twice as long as those of the disc; so 
that only half the number of transverse partitions 
have to be traversed in a given length of a tentacle, 
compared with an equal space on the disc; and there 
would be in the same proportion less retardation of the 
impulse. Moreover, in sections of the exterior ten- 
tacles given by Dr. Warming,* the parenchymatous 
* ‘Videnskabelige Meddelelser de la Soc. d’Hist. nat. de Copen 
hague,’ Nos. 10-12, 1872, woodeuts iv. and v. 
