162 BOTANICAL GAZETTE [FEBRUARY 
When a segment is first cut off from the apical cell, its principal 
wall is approximately parallel to that of the apical cell. The lower 
portion of the segment soon enlarges and the segment assumes the 
shape of a truncated rectangular pyramid, with the smaller end 
above. Transverse sections of the second segment, as repre- 
sented in figs. 8, 9, and 10, show this enlargement of the lower 
portion of the segment. This unequal 
growth of the upper and lower parts 
continues with the further division of the 
a ewan at! cells of the segment. The result of this 
ing eversion produced by Unusual manner of growth is represented 
ual growth of upper diagrammatically by fig. 11. As shown by 
and lower portions of the this diagram, the upgrowth of the periph- 
apical segments . 
eral region and the resultant everted form 
of the protocorm are direct results of the behavior of the segments 
of the apical cell. 
For purposes of comparison, the apical region of an ordinary 
thizome, already described by Hotte (10), was re-examined with 
especial reference to the divisions of the segments of the apical 
cell. In all cases examined, the apical cell is a triangular pyramid, 
as in the protocorm; it measures 120-150 » in length and 30-50# 
across each face at the point of greatest width (figs. 12, 13). Each 
segment divides transversely first, that is, by a periclinal wall. 
Two longitudinal divisions at right angles to each other usually 
follow in the outer cell of the segment. The inner cell of the seg- 
ment may divide in the same way, but more usually the divisions 
are irregular. While the segments cannot be traced to any con 
siderable distance from the apical cell, it is clear that the uppet 
and lower parts of a segment enlarge about equally, in contrast to 
the unequal growth of the parts of the segment in the protocorm. 
Leaves and the sheathing tissue about the leaf bases arise 
from the upper cell of the segment; stem tissue is produced by 
the lower cell. Procambium develops very near the apical cell, 
within the region where the segmentation can be definitely detet- 
mined (fig. 13). In the case figured, it is certain that the vascular 
tissue of the stem is being developed directly from segments ° 
the apical cell, and entirely independent of the leaf traces. The 
