1902] BRIEFER ARTICLES 303 
- obviously from the structure, and when all structural units are evidently 
formed in response to a common stimulus by a similar course of 
growth, then the introduction of the combination of elements as a 
feature distinct from the elements themselves is superfluous and cum- 
_ brous. In this case all the structural elements are similar hair- 
Shaped cells, as stated in two quotations above ; that the stimulus to 
_ the formation of them all was the excess of water hardly admits of 
question. Formed from the original cells which do give rise to them, 
any essentially different arrangement or combination of these elements 
from that occurring is not conceivable. That is, the existing combi- 
nation of the histological elements follows from their origin. The 
imtimate connection of the histological and physiological features is 
mmantly emphasized by Haberlandt ; his whole argument involves 
| this, the “ Zweckmassigkeit ” of the structure. It is possible that the 
_ Seton of the substitute hydathode follows from its structure even more 
intimately than Haberlandt explains. There is nothing difficult to 
2 believe in his supposition that the excretion of water is active on the part 
of the cells.s Such one-sided activity may be manifested in the endo- — 
‘dermis or other cells which force water into the xylem of all plants in 
vaich there is root pressure. And it would be only an assumption of 
tied of the epithem, analogous to many familiar correlations. — 
_ = Sven this use of normally dormant determinants is not altogether 
ag Haberlandt says, “ Auch eine passive Druckfiltration durch © 
a ebenden Zellen der Ersatz-Hydathode ist nicht anzunehmen, da 
‘inzusehen ware, weshalb durch die turgeszirenden Hydatho- 
_ bet das Wasser leichter durchgepresst werden sollte, als durch — 
Hebenden Parenchymscheiden der Gefassbiindel.” Very thin walls : 
_, otoplasmic linings inside them would suggest easy filtration 
‘Pressure; these are characters of the oedemata of tomato to be — 
: Presently, and presumably of the structures in question = ae 
ie i More important than visible difference in the strug : fe 
ence in the turgor. As I have repeatedly shown,’ the 
y cells grow, the less their turgor becomes. In the hy sae oe 
cells of the substitute hydathode there must be a very much» - 
cass,» Pressure than in the cells from which they grew. The 
~~ Pressure in the tracheides at night exerts an equal force to 
ke Sage is open to suspicion, that normal hydathodes act in this way a 
er n Einfus Ss von Licht und Temperatur auf den Turgor- Halle a. S. 
