founded on the Sir uc hire of their Seedlings . 57 
conical sheath formed by the base of the cotyledonary tube. 
The lower part of the tuber tapers off into the primary root. 
Irmisch describes the cotyledonary tube as hollow through- 
out, and speaks of the cavity enclosing the plumule as in 
communication with the outer air through the narrow tunnel 
which opens between the blades of the cotyledons ( 24 , p. 22 1)- 
In the series of sections cut by the microtome through the 
tuber and adjacent parts of three young seedlings, however, 
I find a diaphragm of thin-walled tissue above the extin- 
guisher-shaped sheath which encloses the plumule. The 
narrow bore of the tube itself is far less well outlined in 
transverse section than the plumular cavity, and is separated 
from it by the diaphragm just described. So far as can be 
determined from a number of hand-sections at different levels 
through the cotyledonary tube, it is hollow throughout, but 
one or more diaphragms may quite possibly exist above that 
which seals the plumular cavity. As the tuber increases 
in girth and the plumule in size, the base of the cotyledonary 
sheath is distended, and cracks appear in the diaphragm. 
These fissures may connect the cavities separated by the 
diaphragm, but only towards the end of the season when the 
cotyledons are withering. 
No part of the plumule appears above ground until the 
second season after germination, but at the end of the first 
summer it is no longer embryonic. The first foliage leaf 
is then completely formed and ready to push upwards on the 
approach of spring (Irmisch, 24 , Fig. 15). 
The massive bundles run the whole length of the cotyle- 
donary tube and are continued into the tuber (Irmisch). 
Any one of my three series of transverse sections through 
the tuber shows that it is simply the hypocotyl, swollen 
by the development of the cortex and conjunctive tissue into 
a storehouse for starch and other food-material. The vascular 
system of the first-year tuber is derived exclusively from the 
cotyledonary traces, for during the time that this system 
is developed the plumule is still so embryonic that the position 
of its procambial strands is not even indicated. The process 
