The Phyllode Theory of the Monocotyledonous Leaf, 
with Special Reference to Anatomical Evidence. 
BY 
AGNES ARBER, D.Sc., F.L.S., 
Fellow of Newnham College , Cambridge * 
With thirty-two Figures in the Text. 
PAGE 
I. The ‘ Phyllode Theory ’ from the Standpoint of External Morphology. 
1. De Candolle’s ‘Phyllode Theory ’.466 
2. The relation of the ‘ Phyllode Theory ’ to the theory of the origin of Monocotyledons 
through adaptation to the geophilous habit.468 
3. The relation of the ‘Phyllode Theory’ to the theory of the aquatic origin of Mono¬ 
cotyledons .469 
4. The ‘ Lamina ’ in certain Monocotyledonous leaves.470 
5 . An extension of the ‘ Phyllode Theory ’ to the leaves of certain Gymnosperms . . • 47 2 
II. The Bearing of Anatomical Evidence upon the ‘Phyllode Theory’. 
1. Introduction : 
(i) The nature of the evidence .473 
(ii) The anatomy of Dicotyledonous petioles, phyllodes, and scale-leaves . . . *473 
(iii) Inverted bundles in Monocotyledonous leaves ........ 476 
(iv) Midrib anatomy .476 
(v) TrecuPs Theory . ... . . *477 
2. The occurrence of phyllodic leaf anatomy among Monocotyledons : 
(i) Explanation of list of cases . . . . . . . . . . • 477 
(ii) List of genera in which phyllodic leaf anatomy has been observed among Monocotyle¬ 
dons ............... 478 
3. Notes upon certain of the non-equitant and non-laminate cases enumerated . . .481 
4. The isobilateral equitant leaf and its relation to other phyllodic types . . . .482 
5. Cases of ‘phyllodic’ anatomy which occur among Dicotyledons and the question of 
adaptive interpretations . . . . . . . . . . • *487 
6. The anatomical evidence for Henslow’s corollary to the phyllode theory, with special 
reference to the Pontederiaceae. .488 
7. Certain obscure anatomical features in Monocotyledonous leaves and their interpretation 
on the phyllode theory : 
(i) Strands of fibres ............. 493 
(ii) Apical openings .494 
8. The significance of the systematic distribution of phyllodic leaf anatomy among the 
Monocotyledons .. 495 
III. Summary. ' 
1. External morphology.. . . . • *497 
2. Anatomy .. 497 
Acknowledgements. 499 
Alphabetical list of Memoirs cited ......... • 499 
[Annals of Botany, Vol. XXXII. No. CXXVIII. October, 1918.] 
