292 
Kisch. — The Physiological Anatomy of 
As is to be expected, the meristem keeps pace with the growth of 
the circumference by means of radial divisions (Text-fig. 6). 
(4) Position relative to the Secondary 
Tissue produced. 
Even in young specimens, such as those 
shown in Text-fig. 5, it is generally hard to 
tell in what direction and in what order the 
divisions have taken place, i.e. how much of the 
secondary tegumentary tissue formed corresponds 
morphologically to cork, and how much to 
phelloderm. In older specimens it is quite 
exceptional that the actual meristematic cells 
can still be distinguished with certainty. As 
a result their position has been a matter of 
much speculation, as has been pointed out in 
the historical review. Among recent observers, 
the reasons given by Arber and Thomas, Zalessky, 
and Seward for their determinations of the posi- 
tion of the phellogen, in the absence of direct 
evidence, have already been mentioned. 1 
In the present investigation the lines of split, on which reliance has 
been placed on the ground that the delicate phellogen would form a natural 
Text-fig. 6. Lepidodendron 
selaginoides. Transverse section 
from the outer border of the 
periderm, showing files formed 
by radial divisions in the meri- 
stem to keep pace with growth. 
U. C. L. Coll., A 012. x 265. 
plane of weakness in the stem, 2 have been taken into consideration ; but 
in the specimens examined the position, except in Lepidodendron selaginoides 
2 Seward (28), pp. 107, 115, &c. 
1 Loc. cit. 
