IN VEGETABLE BIOLOGY. 881 
presence of chlorophyll on the free ends of palisade-cells which 
run up into the respiratory chamber is readily conceivable when 
it is remembered that, in consequence of the way in which these 
cells are rounded off, inequalities in the resistance to the trans- 
ference of their protoplasm are obviated or at least minimized. 
Although it is wandering somewhat out of my way, I should 
like to make a short statement with respect to palisade-tissue, 
upon the development of which Stahl* and Pick t have shown 
that light has great influence, the latter going to the length 
ofascribing to heliotropism the frequently observed variations 
from the perpendicular of these cells. Haberlandt f regarded the 
object of the perpendicularity of palisade-cells to be the increase 
in assimilatine capacity, and tbeir arrangement in the leaf the pro- 
vision of a means whereby assimilation-products might be rapidly 
transported to the bundle-sheath. Heinricher §, while agreeing 
with the last-named thatthe assimilating-tissues are so arranged 
with reference to the vascular bundles as to ensure quick passage 
to the latter, finds himself allowed no option but to seek for the 
exciting cause in the intensity of illumination, a view to which 
Haberlandt || has recently subscribed. Both Pick and Heinricher 
are agreed that perpendicularity to the leaf-plane is a hereditary 
character of palisade-cells, the difference between them being 
whether strong light can cause all the distinction between ino- 
diametral cells or cells even elongated somewhat in the direction 
of the leaf’s long axis and typical palisade-elements. Certain of 
Stahl’s and Pick’s figures bear out the view that this can happen ; 
Whereas Heinricher and Haberlandt maintain the effect of light 
to be traceable only in the further elongation of cells already 
having palisade form. The notion of Pick that variations from 
the perpendicular depend upon obliquity in the incidence of 
light is combated by Heinricher, who holds, and apparently 
with reason, that they are the result of dislocations brought 
about by the growth and stretching of other of the leaf- 
tissues. 
* Bot. Zeitung, 1880, and Jenaische Zeitsch. f. Naturwiss. 1883. 
* Bot. Centralblatt, Band xi. 1882, p. 400 &e. 
1 Prings. Jahrb. f. wiss. Bot. xiii. 1882. MN . . 
$ Prings. Jahrb. f. wiss. Bot. xv. 1884. Furtherbibliógraphy will be found in 
9ne or other of the aboye memoirs. 
| Ber. d. deutschen bot. Gesell. 1886. 
