204 MR. 8. LE M. MOORE’S STUDIES 
strongly of the same opinion, in which Pfeffer * has also acqui- 
esced. On the other hand, Prillieux t looks upon the movement 
as resulting from the attraction of one grain upon another, and 
of the cell-wall upon the grains, a curious notion which does not 
appear to have been shared by any otherauthor. Velten f, while 
allowing the great importance of the protoplasmic stream in 
effecting transference of the chlorophyll, considered that the 
grains have some power of moving independentlyof the protoplasm. 
This opinion he arrived at from observing motion round their own 
axis of the grains of two species of Chara; but it seems almost 
impossible to decide that the protoplasm, in which the chlorophyll 
lies embedded, is not the agent whereby this movement is caused. 
Stahl $ leaves the question unanswered, although he seems inclined 
to lean towards Velten’s view, on account of the dependence, as 
respects size and form, of chlorophyll grains upon illumination. 
The reasons which have led me to declare in favour of Sachs's 
theory are the following :— 
(i.) When photolysis is rapid (as e. g. in the cells of insolated 
Elodea leaves before rotation sets in) it is easy to see that the 
velocity of the chlorophyll grains is not greater than that of the 
granules swimming passively in the protoplasm. 
(ii) If Elodea leaves mounted in water and placed under the 
microscope on a warm summer day be exposed to strong illumi- 
nation, the image of the sun being received upon the mirror, 
after two or three minutes the chlorophyll grains will be found 
in rapid motion, either in groups or singly upon the superficial 
or lateral walls. The groups swim in streams of protoplasm, the 
single grains run along fine threads of the same substance. Now 
it sometimes happens that, in consequence of the protoplasm 
streaming in opposite directions in the same thread, pairs of 
* * Pflanzenphysiologie,’ ii. p. 397. 
t Comptes Rendus, 1874, p. 752. 
1 Oesterr. bot. Zeitschr. 1876, no. 3. 
$ Bot. Zeitung, 1880, p. 352. Curiously enough, all authors state that Stahl 
decides in favour of the passivity doctrine. He does nothing of the kind. 
His words are :—“ Die Frage, ob die Körner sich bei diesen Vorgängen ganz und 
gar passiv verhalten oder sich in irgend einer Weise bei den Bewegungen den 
Lichtreize gegenüber thütig erweisen dürfte wohl kaum mit Sicherheit zu ent- 
scheidensein. Die letztere Annahme gewinnt allerdings einige Wahrscheinlich- 
keit bei Erwägung der später zu besprechenden Gestaltsveränderungen von 
Chlorophylikérnern, welche in manchen Fällen ziemlich rasch auf den Lichtreiz 
erfolgen." 
