1804.] Comparative Histology of Pulvini. 479 
pudica. His investigations contradict those of Dutrochet® 
and others. He finds that the impulse normally travels inside 
the collenchyma ring but outside the xylem of the bundles, 
in other words, in the phloem. When a stem is cut, drops 
come from special cellsin the phloem and not from the xylem 
as was formerly supposed. The phloem of Mimosa, like that 
of many of the leguminous plants, is characterized by rows 
of somewhat larger cells than the true sieve-cells, which from 
the nature of their contents are known as tannin cells. He 
concludes that the impulse is transmitted by these rows of 
glucoside cells, and that in a purely mechanical manner. 
his is against the theory of Vines® that the impulse travels 
by the continuity of the living protoplasm, for Haberlandt 
found that the impulse could be transmitted through parts 
that had been killed by steam. : 
A few words in regard to what Vines terms’ the transmis- 
sion of the ‘‘ stimulus.” In accordance with animal physi- 
ology the use of the term is incorrect. It is not the stimulus 
that is transmitted but the stimulus upsets the equilibrium and 
the resulting impulse is transmitted. Heat as heat is not 
transmitted, a mechanical force as such is not transmitted, 
ut each gives rise to impulses that are transmitted. Why 
then in the case of plants like Mimosa is it not the impulse 
from the stimulation which sets off the cells of the succeed- 
ing motor organs and. causes the leaflets to fold together? We 
should speak of the transmission of impulses and not stimult 
and in one more way unify the two sciences. 
In order that we may obtain a correct idea of the move- 
Ments to be dealt with, a short outline of the movements of 
vant organs is here given. Passing by the movements of 
Sfowing organs, or auxotonic movements, which do not | 
Pecially concern us, there are the movements of mature 
= es 
*rgans, or allasotonic movements, which comprise the fol- 
lowing : 
: iti ich 
_ 1. Spontaneous movements, resulting from conditions whi 
© are unable to interpret. 
A 2. Induced movements, or those resul 
d 
% Cording to the nature of the stimulus we 
e 
ting from stimulation. 
distinguish those 
5: 
a eyines; Physiology of Plants 583, 1886. 
i 
84-587. 
a 
Ines; of. cit. 
"Vines: op. cit. 38 
Oye a AER Mee BORER ee ce oat 
ste ake See Ra ; 5 
