I 



,1. -^^,-1 ■ - r- I - - TP 



s. 



OF CERTAIN MONOCOTYLEDONS* 475 



wliich it takes a cylindrical form. Thougli some o£ these apices may, as?! I 

 have suggested^ represent vestigial petioUir tips, in others the thickening 

 may possibly be a secondary development ; each example nmst be judged on 

 its own merits. 



Summary* 



w 



In the present pnper the leaves o£ Monocotyledons are treated from the 

 standpoint of the Phyllode Theor}^ — that is to say, it is assumed that these 

 leaves include no region oquivalentj morphologically, to ilie lamina oi the 

 Dicotyledon. 



It is concluded on the evidence ol comparative morphology and anatomy 

 that, in the case of simple Monocotyledonous foliage-leaves terminating in a 

 solid apex, and also in the case of spathe-leaves ending in a similar tij), the 

 main part of the leaf is of leaf-sheath nature^ while the apex represents a 

 vestigial petiole. 



In the case of those more complex Monocotyledonous leaves which are 

 differentiated into sheath, stalk, aiid '* blade/' certain cases are known in 

 which the ^' blade " terminates in a solid apex. It is provisionally sugge?^ted 

 that such apices represent the unexpanded tip of the petiole : in other words^ 



4 



the main part of the distal region of the leaf-stalk has developed into the 

 " pseuJo-lamina/' while the extreme tij) ha? remained relatively unmodified, 

 retaining its solid petiolar character. 



Acknowledgements* 



I am indebted for material to the Director and to the Keeper of the 

 Herbarium, the Royal Botanic Gardens, Kew ; to the Superintendent of the 

 Oambi'Idge Botanic Garden ; and to the Assistant Curator of the Liverpool 

 Botanic Gardens. I wish also to express my gratitude to Mr. L. A. Boodle, 

 who pointed out to me, some years ago, that the apical structure of Mono- 

 cotyledonous leaves was one of the subjects demanding consideration in 

 connexion with the Phyllode Theory of the Monocotyledonous leaf. 



Bibliography. 



AiiBER, A. (1018). — '* The rii^Uode Theory of the WoiiocotjlcdonouH Leaf, with Special 



Reference to Anatomical Evidence." Ann. Bot. vol. xxxii. 1918, 

 pp. 405-501, 32 text-figs. 

 ,, (1919). — '*Tlie Vegetative Morphology of Pisiia and the LeninaceEe,'' Proc, 



Roy. Soc. Loud. B, vol. xci. 1919, pp. 9G-103, 8 text-figs. 



J, (1920^). — "Leaf-base Pliyllodes among the Liliacese." Bot. Gaz. vol. Ixix, 



1920, pp. 33740, 4 text-figs. 

 „ (1920 ').- '' Tendrils of Smilax^ Ibid. pp. 438-42, 1 pi. 



