Thiselton-Dyer . — Morphological Notes. 755 
would be found in a position peripheral to the whole tube of 
periderm. In the fresh specimen examined for periderm, the 
convexity of individual thick-walled cells was directed away 
from the phellogen ; and as, in Fig. 4, e. w. is the external 
surface of a branch and the convexity of the thick cells is 
turned away from this, the phellogen must have been at the 
surface. The same may be proved by Fig. 3. The external 
walls [e. w., Fig. 4) differed from the other thin walls of the 
same layer in being brownish, and in having similarly coloured 
granules adherent to them. The cells to which these walls 
belong are probably therefore young cork-cells, and the actual 
phellogen has been removed with the cortical tissues. 
The sheathing of internal tissues by a periderm is of course 
a familiar occurrence in other plants, e. g. in the case of parts of 
potato-tubers, when affected by a kind of dry-rot as described 
by Bretfeld 1 . Similar formation of periderm was observed by 
the same author (loc. cit.) enclosing internal tissues injured by 
purely mechanical means in Begonia and Coletis. By means 
of careful torsion of the stem, some of the internal parenchy- 
matous tissues were ruptured without external injury to the 
stem, and after eighteen days the mass of injured cells was 
found to be completely enclosed by periderm. 
For comparison with the periderm-formation around the 
Loranthus - haustorium, an interesting fact, described by 
Arloing and illustrated by him 2 , should be mentioned, 
namely, that the adventitious roots of Cereus monstrosus 
(which branch on their way out through the cortex of the 
stem) are sheathed by a wound - periderm, formed by the 
cortical tissues of the stem, in precisely the same manner 
as has been described in the case of Loranthus - haustoria. 
The root also has periderm of its own. 
To return to the specimen under consideration, it has 
already been mentioned that in most places all the tissues 
lying within the periderm had become devoid of recognizable 
1 Bretfeld, Ueber Vernarbung u. Blattfall. Jahrb. f. wiss. Bot., Bd. xii, 1879- 
Si, p. 138. 
3 Arloing, loc. cit., Fig. 8, PI. 2. 
3 a 
