: and is an especially easy subject for such experimen 
306 BOTANICAL GAZETTE [ APRIL 
Science cannot make a discrimination between the structures on 
Conocephalus and tomato. Both must be regarded as oedemata, and 
it is merely incidental that those of Conocephalus temporarily furnish 
the easiest avenues for the escape of water under pressure. Haber- 
landt tells us truly that drops of water can be forced out through root 
hairs. That happens when the root is in the same condition as the 
Conocephalus leaves. It does not illustrate a “ Zweckmassigkeit” on 
the part of the root hairs. It does not entitle them to be regarded as 
organs of excretion, emergency hydathodes. But there is only the 
same ground for calling the Conocephalus oedemata “ organs,” when 
they are of incidental temporary utility. 
The position of the ‘substitute hydathodes,” which Haberlandt 
regards as a striking feature, has not been discussd. They must be 
formed on the veins, because, as in the tomato, the water is mot oe 
sive there. And their appearance under old colleters is at the pots 
of least resistance, where the cuticle is already ruptured and the walls 
have been partly softened. Atkinson says that oedemata on Us 
tomato stem are formed in places where there are already large cells | 
and “their walls are less resistant.” If the oedema cells are ine 
_ more slender in Conocephalus, as the figures would indicate, it iswhat 
_ should be anticipated from the firmer texture of the leat 
__'The tomato has so far been used alone to furnish means 
‘par: it has been well worke® © "® 
parallel to that of Conocephalus, because it h te. There att 
tions the fact 
_ Bumerous other known illustrations. Haberlandt men 
_ that Sorauer describes “ Pathologische Veranderungen der 
verschiedener Pflanzen, welche mit dem Bau der Ersatz-Hy gee 
von Conocephalus eine gewisse Aehnlichkeit besitzen.” Afterremar” 
_ ing the absence of proof that these structures are caused D’ . 
water (which proof has been given for the tomato), Haberlanct : 
that they may be ‘“Analoge Erscheinungen - - - - — a gma - 
Ansatze zu einer Selbstregulation, die bei unserer Pflanze gan? oF 
mittelt in so vollkommener Weise sich einstellt.”’ es 
2 : ; L : on le ak 
xcessive moisture acts in the same way elsewhere tan 
___ SATKiNson, G. F., Oedema of apple trees. Rep. A8™ a 
3893, pp. 305-307. ae 
