370 



MR R, C. DAVIE ON 



even the last pair of pinnae, in order to provide sufficient water-supply for the " tail " 

 of the leaf. # The two exceptions, Balantiwm culcita and Dicksonia fibrosa, have 

 relatively short leaves with pinnse situated at greater distances from one another 

 than are those of Cyathea, Alsophila, and Hemitelia. And these two have only 

 slight hooks on the adaxial faces of their leaf-traces, a much simpler type of leaf-trace 

 and marginal supply to the pinnse. 



An interesting confirmation of this view of the function of the incurved margins 

 of the leaf-trace comes from Botrychium virginianum (Chrysler, '10). There the 



Ticxr- Fig. 1 1. — Botrychium daucifolium, Wall. Diagrams illustrating the departure of the vascular supply 



to the first pair of sterile pinnse. 



margins of the leaf- trace strands nip off, pass along the adaxial face for a short 

 distance, and then take up the position of margins for the leaf-trace when the pinna- 

 trace goes off. This ensures a continuity of water-supply past the bases of the 

 pinnae. Botrychium daucifolium, Wall., affords us an example of a similar process 

 (text-tig. 1 I ). In the preparation for the departure of the vascular supply to the 

 first sterile segments of the leaf there appears on the inner side of one of the two 

 lea I'-t race strands at first a single tracheide, then a small group of tracheides (text- 

 fig. I I, b), which approaches the leaf-trace strand and finally unites with it (text- 

 fig. I I, <■). Part of the group then goes off with the portion of the leaf-trace strand 



* See also Diplazium marginatum, where the supply is marginal to the nerve fourth in position from the ti j> 

 of the leaf. 



