1914] PETRY—OPHIOGLOSSUM PENDULUM 183 
bud or not. In the lowest part, the cylinder is already definitely 
organized and of the full diameter. There are five gaps corre- 
sponding to leaves that were no longer attached, and 18 leaves 
were still in position. This is almost certainly the oldest specimen 
secured. 
Up to the level of the fourth leaf gap, the stem cylinder agrees 
in all details with the usual form, as described above; but about 
midway of the gap, a strand of xylem separates from the margin 
of the gap, swings over to the center of the opening, broadens, and 
by connection with the xylem at either side closes the gap. The 
gap of the sixth leaf is closed by a similar strand. The gaps of the 
fifth and seventh leaves are closed in a similar manner by strands 
which arise as procambium in the parenchyma of the openings. 
At the level of the fourth leaf, a strand separates from the inner 
surface of the cylinder opposite the point of connection of a root. 
This strand runs in the pith near the middle of the cylinder for a dis- 
tance of about 4.5 mm. and finally closes the gap of the eighth leaf 
In the manner described. In addition to these five strands, there 
are in this portion of the stem seven others which arise as pro- 
cambium or by separation from the inner surface of the cylinder and 
disappear in the same way, without being in any way related to 
leaf gaps. One of these closes an incidental gap of the cylinder. 
From the level of the eighth leaf to that of the twelfth, there 
are no medullary strands, and the stele presents the usual appear- 
a At this point another system of seven strands appears; 
their positions and behavior are shown in fig. 12. Between the 
Seventeenth and twentieth leaves, no medullary strands occur; 
ut at the level of the latter, three more strands appear as pro- 
Cambium in the pith. One appears in the opening caused by the 
twenty-first leaf and closes that gap; another appears in the center 
of the base of the twenty-second leaf, and moves inward and closes 
the gap. The third, arising near the center of the cylinder, branches 
once or twice; one branch is recognizable as a procambium strand 
at a short distance from the apical region. 
In all, 23 medullary strands occur: 16 arise as procambium in 
the pith, 5 as branches from the inner surface of the cylinder, and 
2 as branches of other strands; 9 of them are concerned in the 
