r ■ 



468 ON THE LEAF-TIPS OF CERTAIN MONOCOTYLEDONS. 



solid cylindrical apex, corresponding to tlio basal part of the petiole in the 

 fully-developed leaf *. In its form anri anatomy^ and in its relation to 

 the leat-sheath, this apex exactly recalls iliat of Tnlipa sf/Ivestris^ etc. In 

 the present paper, a more extended study of leaf-apices is nndertakcnj in 

 order to determiuo whether the explanation advanced for Tulipa sylvesfns 

 is capable of general application to Monocotyledonous leaves with cylindrical 

 tips. 



Monocotyledonous leaves with solid apices fall into three categories : 

 simple foliage-loaves with no differentiated limb ; spathe-leaves ; folinge- 

 leaves with *' pseudo-laminoe.'^ AVe will consider these in order. 



1. Foliage-leaves of the Type 0/ Tulipa sylvestris, L. 



Leaves of the type ol TuUpa si/Ivestris have a sheathing parallel-veined 

 limbj terminating in a cylindrical apex. The ^Yild Tnlip is uot an isolated 

 case, for such leaves occur in a number of the Liliiflor;Te. In this Cohort we 

 can trace every gradtttiou from leaves which — on my interpretation — arc 

 petiolar })hyllodes in which the sheathing base is relatively unimportant 

 to leaves which are mainly of leaf-sheath nature, but terminate in the 

 tiniest rudiment of a vestigial petiole. It is the latter type of leaf which 

 specially concerns us here. In the Liliacea) I have already recorded the 



existence of a solid cylindrical tip in the 

 while Dracicha t (figs. 2-i) and Corduline 



ft 



t 



X 



(fig, 7) in the Hremodoracen?, Doryanthes^ (fig. 1) and Fuvcrwa in the 

 Amaryllidacere, Mora\i |I in the Irilaceoe, and Distichia (fig, G) in the 



FJe 



L- 



Juneacece, supply comparable cases. This Ij'pe of leaf is, however, by no 

 means confined to the Liliiflora?; among the Farinosro it forms a conspicuous 

 feature. Leaves resombliii 



(fig, 5), Fedio^ Lepi/rodia^ ijejytocarpvs (^itesLuice?ej, ami are round, ttiouo-ii 

 less ty])icully developed, in certain species of Jiromelia {fig. 8), and Tillandsia 

 (fig. 9) (Bromeliaceae). 



The anatomy of these solid apices sup}>orfs the petiolar interpretation. 



GoobclH has described the occurrence of a bundle-ring lu the leaf-tip of 

 Forj/avOd's Pahneri^ W, Hill, and I have found the siuno structure in 

 D. Guilfoylei^ W. M. 13aile3\ The solid apex in this species is developed 

 on a very conspicuous scale (fig. 1) ; in the plants grown at Kew it may 

 be more than 0'5 cm. in diameter. In the apex of Draccrna Fraco^ L. 



* ArLer, A. (19l'0^), figs. 1 a, b, c, p. 339. 

 t Arber, A. (1920^). 

 X Velenovslvj, J. (1907). 

 § Goebel,K, (1901). 



Ross, II. (1892-3), Arber, A. (1921). 

 ^ Goebelj K. (1901). 



I 



