iQ2o] ARBER— TENDRILS , 439 



If any of these related alternatives held good, we should expect 

 to find the vascular structure of the tendril showing some affinity 

 with the vascular structure of the midrib or lateral veins of the 

 "lamina" of the Smilax leaf. The midrib and lateral veins of the 

 blade, however, are each characterized by an arc of bundles (fig. 4), 

 while the tendrils have an irregular closed ring (fig. 3B). 



4. That the Smilax tendrils are metamorphosed trichomes or 

 emergences. 



The high development of the vascular system of the tendrils 

 seems to make it impossible to accept this theory. The emergences 

 on the stem of Smilax itself, which on this view must be homol- 

 ogous with the tendrils, are non- vascular, as are the paired glands 

 at the base of the leaf of Tamus communis L., whose position at 

 first glance suggests a comparison wdth the tendrils of Smilax. 



5. That the tendrils of Smilax represent "un double prolonge- 

 ment lateral des elements cellulo-vasculaires du petiole." 



This view, which was suggested by Clos (2) more than half a 

 century ago, and has been more recently supported by Gluck (5), 

 seems to contain the germ of the true explanation, although, in the 

 form in which Clos enunciates it, it is essentially descriptive rather 

 than morphological. The writer wishes to propose a related but 

 more comprehensive view, which interprets each of the tendrils of 

 Smilax as equivalent in morphological value to the petiole, and as 

 having originated through a dedoublement or chorisis of that organ. 



An analogy may perhaps be suggested with the stamen pha- 

 langes of Hypericum Elodes Huds., which sometimes consist of three 

 members, and which very probably have arisen by secondary 

 chorisis of an ancestral single stamen. A closer analogy is indicated 

 by Queva's (7) comparison between the anatomy and insertion 

 of the tendrils of Smilax and the stalks of the leaflets of certain 

 Dioscoreaceae with compound leaves. It seems by no means 

 impossible that, in this family, the compound character of the leaf 

 may also be due to chorisis of the petiole giving rise to three equiva- 

 lent organs. 1 



1 The writer hopes to deal in a later paper with the general subject of "compound" 

 leaves among monocotyledons, and to discuss the part which chorisis may have played 

 in their origin. 



