IN VEGETABLE BIOLOGY. 885 
systrophe, a weaker one epistrophe; but a still weaker one causes 
—not an enhancement of epistrophic action, as ought to happen— 
but precisely the same result asa strong stimulus! Then there is 
that crue epistrophe (as of Elodea &c.) in darkness. The chlo- 
rophyll of Elodea is positively apostrophized, with or without 
rotation supervening; the plant is then set in darkness, and 
after being thus treated with a double dose of apostrophizing 
stimuli, epistrophe, strange to say, is the result! But perhaps 
it is not necessary to carry this criticism further. 
Where Schimper really traces phototaxy, viz. in the turning 
edge-up of the chlorophyll grains, I am quite unable to see any- 
thing but adaptation to pressure. To take a case cited in the 
previous memoir,— a rotating stream in an Elodea-cell moving, as 
occasionally happens, for a short part of its course upon either 
the upper (outer) or lower (inner) wall. When upon a side-wall 
the grains are set edge-up to an observer, but immediately upon 
their arrival at that spot where the plane of rotation changes, 
they turn over upon their broad side. How can phototaxy be in 
point here, seeing that when the grains arrive upon a more 
highly illuminated wall, they expose themselves more to the sun’s 
Influence than was the case before? It will possibly be allowed 
that this and other considerations urged in the previous memoir, 
and which there is no necessity to repeat, are a sufficient answer 
to Schimper upon this head. 
Neither does the notion anent the gaseous relations of the 
grains seem free from objection. Itis not the case with a large 
number of cells, e. g. the palisade-tissues, that when the grains 
are exposed to epistrophizing grades of illumination, and are 
ranged upon the walls bounding intercellular spaces, they shift 
on to other walls when light becomes too strong. Indeed, 
Haberlandt’s doctrine, previously referred to, is based upon a 
directly contrary statement, viz. that the septa of palisade-cells 
are free from chlorophyll, which must consequently line the walls 
bounding the respiratory chamber or spaces connected there- 
with ; and we know that when the grains of these cells mass, 
in almost all cases they meet upon some part of the side of the 
Cell, not upon one of its transverse walls. This does not apply 
to the mesophyll-cells *, the chlorophyll of which does shift on 
* Exceptions to this are some succulent types. Thus Stahl (Bot. Zeitung, 
1880, p. 340) found the chlorophyll of the mesophyll-cells of Sedum dasyphyl- 
lum upon the walls bounding intercellular spaces after an hour’s insolation. 
Schimper must tell us how it is that these grains escape destruction. 
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ai i SR i ND. 
