380 MR. S. LE M. MOORE'S STUDIES 
grains of palisade elements shift their position in feeble light. 
Now in the case under notice Haberlandt found the grains col- 
lected upon the walls bounding intercellular spaces, that is on 
the concave walls ; and it is here that, upon the mechanical doc- 
trine advanced in the previous memoir, friction being at its 
maximum, we should expect massing to occur*. It is therefore 
my belief that Haberlandt’s specimen was examined under too 
high or too low a grade of illamination t; in fact, substantially 
the same arrangement is shown in figs. 8 and 9 of my previous 
memoir. The fact of the departure of chlorophyll from lateral 
septa taking place not only in sunlight, when assimilation is 
enhanced, but in darkness, when it is in abeyance, proves that 
transport of assimilated material is in no way related thereto. 
But if Haberlandt’s doctrine must be rejected, however inge- 
nious it may appear, and if Stahl’s apostrophe notion meet with 
the same fate, what theory will explain the facts of the case? The 
answer is that the protoplasm in the course of its redistribution in 
a cell moves in the direction of least mechanical resistance. provided 
the attracting or repelling action of light impose no obstacle to such 
movement. It was Velten t who some years ago started the least- 
resistance notion in explanation of the constancy of the plane of 
the rotating protoplasm of Elodea &c.; and the same reason may 
be adduced for the arrangement of the chlorophyll upon the 
upper and the lower wall when rotation has ceased. So, too, in 
a palisade-cell with massed chlorophyll; when illumination again 
becomes favourable, the heaped protoplasm tends to fill a wider 
area, and in so doing moves where it finds least resistance to its 
passage. Now the grains mass upon the side of palisade-cells, 
only exceptionally upon a transverse wall$; so that when the 
protoplasm streams out, the coefficient of friction of the moving 
mass against the stationary limiting layer will be highest where 
the side i is cut by a transverse septum, and still relatively high 
at the point of junction of the side with an oblique septum ; 
hence the absence of chlorophyll from the septa. Moreover, the 
* Tam inclined to extend this notion so as to embrace all cases of massing 
or apostrophe upon the walls bounding intercellular spaces. As cases in point, 
see figs. 1 and 5 of Haberlandt’s 1886 memoir. 
t Perhaps the sectioning practised by Haberlandt tended to drive the grains 
from the septa more rapidly than would otherwise have been the case. 
1 Flora, 1873. 
$ As is admitted by Haberlandt himself (see 1886 memoir, p. 210). 
