462 Arber . — -On the Leaf Structure of certain Liliaceae , 
prasiMt (Figs. 24 A and B, p. 457), while in Arnocrinum Drummondii 
(Fig. 16 A, p. 454) the median bundle is less well developed than the 
laterals on either side of it. In the isobilateral equitant leaf of Tritonia 
(Iridaceae) the main laterals are again the predominating strands. 1 I know 
of no parallel for the condition in A. Solandri , &c., among Dicotyledonous 
laminae, but the petiolar phyllodes of certain Acacias show just the same 
relation of a small median bundle to large main laterals. 2 Though the 
great majority of petioles have a midrib, Petit 3 has drawn attention to its 
absence in certain cases, and its relative insignificance in others. In the 
petiole of Antigonon leptopus , Hook, et Arn., for instance, the midrib bears 
much the same, relation to the laterals 
3 5. Antigonon 
m. L b . 
1. .... 
1h 
\ 
Vn 
..H 
fnb / 'S 
tf-\z 
34 . 
.b. 
Asielia 
Figs. 34 and 35. Fig. 34, Astelia So- 
landri , A. Cunn. Transverse section of limb of 
leaf (x 23); m.b., median bundle; and A 
laterals ; fibres. Fig. 35, Antigonon lep- 
topus , Hook, et Arn. (Polygonaceae). Trans- 
verse section of petiole for comparison with 
Astelia, showing small size of main bundle 
(m.b.) in comparison with the laterals (l x and 
/ 2 ) ; m.i.b. = main inverted bundle. ( x 14.) 
as in Astelia (Fig. 35). It seems to 
me possible that, in emphasizing its 
main laterals rather than its midrib, 
the leaf of Astelia is revealing a symp- 
tom which would more readily develop 
in a phyllode — whether of leaf-base 
or petiolar nature — than in a true 
lamina. 
Through the kindness of Dr. 
Greenman, of the Missouri Botanical 
Garden, I have been able to examine 
the leaf anatomy of a series of species 
of Dasylirion : D. acrostichum , Zucc., 
D. cedrosanum , Trelease, D. glauco- 
phyllum , Hook., D. graminifolium , 
Zucc., D. leiophyllum , Engelm., D. 
longissimum , Lem., D. lncidum 9 Rose, 
D. P aimer i, Trelease, D. serratifolium , Zucc., D. texanum , Scheele, and 
D. Wheeleri , S. Wats. 
Dasylirion longissimum (Fig. 36) has a centric leaf, but all the other 
species enumerated are more or less flattened, e.g. D. Palmeri (Fig. 37). 
The anatomy of the limb of the leaf is essentially uniform throughout these 
eleven species and all the main bundles are normally orientated ; though 
some of the smaller bundles are irregularly placed, there is no series 
of strands with inverted orientation. In general there is a series of 
large bundles (b i) lying towards the upper surface, and a series of smaller 
ones towards the lower surface ( b II). Sometimes a third series of smaller 
bundles {b III) lies close to the upper surface (e. g. D. longissimum , Fig. 36). 
There may be a number of irregularly orientated bundles ( b IV) in the 
parenchyma in the middle of the leaf, and also a number of similar strands, 
1 Arber, A. (1918), Fig. 15 b, p. 483. 2 Ibid., Figs. 2 B, c, D, p. 474. 
3 Petit (1887 and 1889). 
