'I'llli ANGIOSPKRMAE: LEAVES (^97 



stipules are formed. The developmental history, therefore, supports the view 

 that the phyllode is simply a broadened petiole. 



Fig. 983. — Oxalis bilinibi. Young plant 

 showing transition from ternate 

 leaves to phyllodes. 



A. P. de Candolle in 1827 raised the question whether the linear outline 

 and parallel venation which distinguishes so markedly the leaves of Monoco- 

 tyledons might not be due to their phyllodic nature. This view has been 

 strongly upheld by Arber, who bases much of her argument on anatomical 

 grounds, especially the widespread occurrence of vascular bundles with 

 inverted orientation on the adaxial face of the " leaf." The broadened lamina 

 which occurs in many Monocotyledons {e.g., Alisma, Arum, Tamus, etc.), 

 she interprets as due to a secondary expansion of the apex of the petiolar 

 phyllode, and she further comments that the prevalence among such cases 

 of simple lanceolate or cordate shapes indicates an origin distinct from that 

 of the multiform laminae of Dicotyledons. Even among the Monocotyledons 

 which have leaves with a lamina and a petiole, e.g., the Araceae, the phyllodic 

 tendency shows itself in the frequent lateral expansion of the petiole, associated 

 with the diminution of the lamina, so that the leaf blade is formed of two 

 portions, one above the other, which may be either separate or more or less 

 confluent. There can be little doubt that the leaves of many Monocotyledons 



