158 BOTANICAL GAZETTE [FEBRUARY 
would produce a structure differing in only two important par- 
ticulars from the vascular cylinder of the protocorm: (1) the 
leaf trace of the inverted cylinder of the rhizome would be a single 
bundle; the leaf trace of the protocorm consists of two bundles; 
(2) the roots of the everted cylinder of the rhizome would be 
within the cylinder; in the protocorm, with three exceptions, they 
are outside. 
Fics. 3, 4.—Fig. 3, model of the vascular system of the protocorm, from the 
side: f, bundles of the functioning leaf; x, position of apical cell; <8; Fig. 4, model 
from the side at right angles to fig. 3. 
As indicated by this illustration, the oldest portion of the 
cylinder is at the top of the corm and the formation of new vas- 
cular tissue proceeds in a downward direction. There is a gap in 
the cylinder corresponding to each leaf; no gaps not definitely 
related to leaves occur. The gap is below the point of attachment 
of the leaf bundles, as would be the case in the everted cylinder ot 
a rhizome as described above. On either side of a gap a strand 
runs downward in a nearly vertical direction for a short distance 
