3 1 8 
Harriet E. Allison. 
In order to study the relations of the leaf-trace to the vascular 
system of the axis, serial sections were cut through the insertion 
of three leaf-bases, two being foliage and the other a nest-leaf. 
The lowest of the three leaf-traces proved to he that of a nest- 
leaf (Fig. 4, 1-20). Preparations for the formation of the leaf-trace 
in the axis are seen in the expansion of the dictyostele by division 
and elongation of the meristeles to form a kind of pocket (Fig. 4* 
2). Gradually the dictyostele widens, the strands elongate and 
finally divide into several strands, which form the outer ring of 
bundles in the petiole. While this gradual expansion has been 
taking place in the outer ring, some of the medullary bundles 
opposite the departing leaf-trace have divided, and these go out 
as the internal bundles of the leaf-trace. As in the axis, some of 
the internal accessory bundles are formed by splitting off from 
the outer bundles (Fig. 4, 6, 7). The leaf-trace is now complete 
and passes out into the nest-leaf, the short petiole showing an 
external ring of strands and a small number of internal strands. 
As this kind of leaf is almost sessile, the bundles on the outside 
of the petiole extend very soon by division or elongation into the 
expansion of the leaf. The leaf-gap is closed by the elongation of 
one or two of the accessory bundles to form a transverse com¬ 
missure (Fig. 4, 75-/7). This is comparable with what is seen in 
the solenostele of Acrostichum anreum (Thomas, II; Tansley, 10), 
and also in the dictyostele of Angiopteris evecta (Shove, 9), where 
the gaps are filled by medullary bundles. For some time one side 
of the leaf-trace remains connected with the main dictyostele, a 
condition not unusual in dorsiventral shoots of ferns. 
When this commissure is formed across the leaf-gap of the 
next leaf, the dictyostele shows signs of preparation for giving off 
another leaf-trace (Fig. 4, 17-32). As in the case of the nest-leaf, 
the meristeles in that region begin to divide and the whole ring 
expands. The internal bundles also become more numerous and 
pass into the gap left by the enlarging dictyostele (Fig. 4, 18-21). 
Thus a pocket is formed with a ring of almost equidistant strands 
on the outside, while internally, in this case, there are three 
accessory strands, which divide to form the medullary bundles of 
the petiole. Soon the pocket becomes constricted by an intrusion 
of sclerenchyma, which takes place from one side only, the other 
side remaining connected as in the nest-leaf. Finally, when the 
constriction is complete, the outer strands of the trace divide and 
thus complete the outer ring of petiolar strands (Fig. 4, 26-33). 
