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ON THE LEAF-TIFS OF CERTAIN MONOCOTYLEDONS. 



467 



On the Leaf-tips of certain Monocotyledons. By Agnes Arber, D.Sc, 

 F.L.S., Keddey Fletclier-AVarr Student of the University of Loudon. 



(With UText-flgures.) 

 [Read 3rd February, 1921.] 



Contents. • p^^^ 



Introduction •. ■ '*"^ 



1 . Foliflge-leaves of tlio Type of Tulipa si/Ivestris, L 468 



2. Spiithe-leaves of the Type of Ludovia cremfolia, Drudc 471 



3. rseiido-lainiiKic of the Type of Smila.v aspera, L 472 



Summary 



Acknowledgeineiita 



Bibliography 



476 



475 

 475 



Introduction. 



It has lono- been known that a number of dorsivcntral leaves among 

 Monocotyledons are sliglitly hooded at the tip of the limb, and terminate in 

 a solid cylindrical apex, sometimes of considerable length, but sometimes so 

 short as to escape general attention. The question of the hiologual value of 

 the leaf-apices of Monocotyledons has been considered by various authors 

 in connection with " drip-tips " * and with the extrusion of water f, 

 while Goebel X, who has made a special study of certain of those cylin- 

 drical apices with which we are here more particularly coneorned, regards 

 them as oro-ans serving for bud-closure ("plug-tips") and also for re- 



s' — ' •" o 



spiration. But although in their teloological aspect these structures have 

 received so much notice, their morphological interpretation seems never to 

 have come under discussion. In a recent paper §, as a result of studying 

 the leaves of certain Liliaceaa from the standpoint of the Phyllode Theory, 

 I have suo-o-ested that, in Tulipa sijhestrU and one or two similar cases, the 

 main part of the leaf is of leaf-shcath nature, while the solid apex is to be 

 reo-arded as a vestigial petiole— the lamina being altogether unrepresented. 

 The interpretation was based upon a comparison with the bud-scales of the 

 Dicotyledon, Fatsia japomca, Decne. & Planch. In this plant, among the 

 transitional leaf-forms between the bud-scales, wliich are of leaf-base nature, 

 and the mature foliage-leaves, we find sheathing leaves terminating in a 



* Jungner, J. R. (1891), Stahl, E. (1893). 



t Volkens, Gr. (1883), Minden, M. von (1899), etc. 



X Goebel, K. (1901) and (1905). 



§ Arber, A. (1920^). 



K 



