The Leaf Structure of the Iridaceae, considered in 
Relation to the Phyllode Theory. 
BY 
AGNES ARBER, D.Sc., F.L.S., 
Keddey Fletcher- Warr Student of the University of London. 
With sixty-six Figures in the Text. 
Contents. 
PAGE 
1 . Introduction . . . .301 
2 . Ensiform Petiolar Leaves . 302 
(i) The occurrence of ensiform 
leaves in the Iridaceae . . 302 
(ii) Views hitherto held on the nature 
of the ensiform leaf . . 303 
(iii) The ensiform leaf as a petiolar 
structure, and the comparison 
with Acacia phyllodes . . 303 
(iv) Semi-equitant leaves . . 306 
(v) The association of ensiform leaf 
and winged axis in certain 
Monocotyledons and Acacias . 308 
3 . Non-ensiform Leaves in certain 
Iridoideae 310 
(i) * ‘ Radial ’ leaves in Iris and other 
Iridoideae, and their relation 
to Acacipt. phyllodes . . 310 
(ii) Transitional and bifacial leaf- 
types in Iris and Moraea . 312 
PAGE 
4 . Leaves of the Ixioideae and 
Phyllodes of Acacia • . . 317 
5 . Fibrosis in Irids and Acacias . 319 
6. Foliated Leaves in the Iri- 
doideae and Ixioideae . . 320 
7 . The Leaves of the Crocoideae. 323 
8. Asymmetry in certain Irid 
Leaves 328 
9 . The Evolutionary PIistory of 
the Irid Leaf .... 329 
(i) The primitive character of v the 
ensiform leaf-type . . .329 
(ii) The progression from the ensi- 
form leaf-type . . . 331 
10. Summary 333 
Alphabetical List of Memoirs 
cited 335 
i. Introduction. 
T HE present paper forms one of a series 1 in which I am attempting to 
test the validity of the phyllode theory by studying the results of its 
application to the leaves of various groups of Monocotyledons. In this 
instalment I propose to deal with the Iridaceae — that family in which, on 
my view, the phyllodic leaf finds perhaps its most varied and complete 
1 ‘Arber, A. (1918), (1919 1 ), (1920 1 ), (1920 2 ), (1920 3 ). 
[Annals of Botany, Vol. XXXV. No. CXXXIX. July, 1921.] 
X 
