Morphology of the Leaves of Palms. 



257 



« plication " of the limb, fail, at their proximal limit, to reach the epidermis 

 either on the ventral or dorsal side, so that part of the petiolar surface is, in 



Fig. 6. — Trachycarpus excelsus, H. Wendl. Ventral view of junction of leaf-limb 

 and petiole to show " ligule " or ventral crest, v.c. ( x £). 



Fig. 7. — Rhupis humulis, Blume. Series of transverse sections through young leaf 

 of mature plant, passing through junction of petiole and leaf-limb from below 

 upwards ( x 9, circa) ; fig. 7, A, top of petiole ; in fig. 7, B, invagination is just 

 beginning and the slightly developed " dorsal scale " or dorsal crest (d.c.) is 

 distinguishable ; in fig. 7, C, the "ligule *' or ventral crest (v.c.) is just becoming 

 detached, while in fig. 7, D, it is entirely free. The asymmetry of fig. 7, B and C, 

 is due to a slight obliquity in the series of sections. 



•each case, left overarching the base of the limb. This produces the " dorsal 

 scale " at the back (fig. 7, B, d.c), and the more prominent " ligule " on the 

 ventral side (fig. 7, C, D, v.c). The hooded tip of the plumular leaf of 

 Pritchardia filifera (fig. 5, E) is a comparable case on a smaller scale, though 

 here it is the distal end of the median invagination which is overarched by 

 the ventral surface of the limb. . I think it will be agreed that the almost 

 cup-like form produced in Trachycarpus excelsus by the base of the limb and 

 the " ligule " together .(fig. 6), is consistent with the view that the " ligule " 

 merely represents the limiting region of the uninvaginated proximal part of 

 the petiole. 



The bearing of the interpretation of the " ligule " and " dorsal scale," 

 which I have just outlined, upon the homologies of the Palm leaf, will be 

 considered in the next section of this paper. 



III. The Morphological Nature of the Palm Leaf. 



There has never been any question among botanists as to the nature of the 

 sheath which forms the extreme base of the Palm leaf ; its homology with 



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