IN VEGETABLE BIOLOGY. 205 
grains approach and clash, one of them turning by this means 
upon its edge and being thus enabled to pass its fellow. When 
the grains clash, a large part of their momentum must disappear ; 
and if they were not passively drifting along, some appreciable 
slowing of their speed should be observed, because time would 
be required for the regeneration of that part of the lost momentum 
due to their own proper motion. But such retardation does not 
occur, for almost immediately after impact the journey is resumed 
at its former rate. 
(ii. If light acts directly upon the grains it might be expected 
that they would sometimes spontaneously turn upon their own 
axis. I have failed to detect any instance of this movement 
which was not referable to some external cause. 
Is the Movement transmissible ? 
A question of some interest is broached when it is asked 
whether, in view of Strasburger’s theory of the universal conti- 
nuity of protoplasm* and the undoubted fact that effects ascribed 
to the action of light are capable of transmission from one part 
of a plant to another t, the slow movements of protoplasm which 
cause the chlorophyll grains to change their position are also 
themselves transmissible. In order to answer this question, the 
following experiments were made. 
Leaves of Funaria hygrometrica which had remained four days 
in darkness were placed in a shallow gutta-percha dissecting-tray 
half-filled with water ; to the bottom of the tray was closely pinned 
a piece of cardboard, in such a way that while completely covering 
some of the leaves, others were left half exposed, the latter being 
retained in position by means of a small pin passed through their 
apex. Examined after three hours’ exposure to good diffused 
light, the chlorophyll of the covered leaves being in apostrophe, 
that of the others was in apostrophe where covered, in epistrophe 
where uncovered, with a sharp line of demarcation between epis- 
trophe and apostrophe. . 
In order to avoid any error which might have arisen from 
insufficiency of time, the experiment was repeated with leaves 
set in darkness overnight, allowing six hours instead of three for 
transmission to declare itself, but the result was precisely as 
* Vide ‘Bau und Wachsthum,’ the section headed “ Die Wegsamkeit der 
Zellhäute " (p. 246). 
t As for instance in “ sensitive" plants. 
