493 
the Monocotyledonous Leaf \ 
the aerial and floating * laminae ’ of Hydrockaris, Limnobium, sx\d Hydro- 
my stria} Solereder, to whose work on this Family we have already referred, 
regards the Hydrocharitaceae as unique in this respect, but the present 
writer has, as has just been shown, found comparable cases in the Ponte- 
deriaceae and Alismataceae. As we have already pointed out, Solereder 
recognizes that the anatomy of the lamina in the Hydrocharitaceae is 
petiole-like—he says: ‘ Es ist eben einfach Blattstiel- oder Blattscheiden- 
struktur’—but he leaves this peculiarity as an unexplained parallelism and 
draws no conclusion therefrom. 
The present writer recognizes that, in spite of the anatomical evidence 
here adduced, Henslow’s corollary to de Candolle’s theory rests on a 
slenderer basis of evidence than the main theory itself. It is apparently 
open to us at present to hold one of several alternative views. De Candolle’s 
theory may be accepted, while Henslow’s corollary is entirely rejected, or 
Henslow’s view maybe accepted as far as the Pontederiaceae are concerned, 
with the reservation that the ‘ laminae ’, occurring elsewhere among the 
Monocotyledons, may, in some or all cases, have had a different origin. 
Or, finally, the view may be taken that the Monocotyledons are all 
descended from a stock in which the lamina had been entirely lost and that 
the existing Monocotyledonous blades, whether showing inverted bundles or 
not, are all ‘ pseudo-laminae ’ of later development. This is the view held 
by the present writer, but slje realizes that a complete proof is still lacking 
and that the theory must at present be treated as provisional only. 
7. Certain obscure anatomical features of Monocotyledonous leaves 
and their interpretation on the phyllode theory. 
(i) Strands of fibres. 
In some Monocotyledonous leaves, besides the vascular bundles, longi¬ 
tudinal strands occur consisting exclusively of fibres. Potamogeton zosteri- 
folins , Schum., furnishes a striking instance of this. One of the figures given 
by Raunkiaer 2 of the leaf of the winter bud of this species shows, in 
transverse section, a midrib and four lateral vascular bundles situated about 
half-way between the upper and lower surfaces of the leaf, while, in addition 
to a thick strand of fibres close to each margin, there is a series of twenty- 
five fibrous strands near the upper surface and a second series of sixteen 
fibrous strands near the lower surface. It seems conceivable that these 
fibrous strands are derived from ancestral vascular bundles, which have lost 
their conducting tissue and become reduced to fibres alone. The develop¬ 
ment of fibres in association with the vascular bundles of the leaves of 
Monocotyledons often occurs on a most remarkable scale ; the xylem and 
phloem in the leaf-bundles of Agave densiflora (F'ig. 13, p. 479 ), for instance, 
1 Solereder, H. (1913). 2 Raunkiser, C. (1896), p. 88, Fig. 49. See also p. 62, Fig. 27 b. 
K k 2 
