49 & Agnes Arber .— The Phyllode Theory of 
as a special case of phyllodic structure (p. 48a). It is shown that this type of 
leaf is widely distributed among the Monocotyledons, that it can be closely 
compared with certain Acacia phyllodes, and that transitions can be traced 
between it and other types of Monocotyledonous phyllode. 
It is suggested that certain examples of ‘ radial \ leaf anatomy among 
Dicotyledons may possibly be explained on lines similar to those indicated 
for the case of ‘ phyllodic 5 Monocotyledons. It is proposed that, in lieu 
of regarding a centric leaf with peripheral bundles as an adaptation to 
xerophilous life, it may be more logical to interpret this type of anatomy as 
an hereditary indication of the phyllodic (or midrib) nature of the leaf; that 
it happens to be one of the features which may enable the plant possessing 
it to become a xerophyte, is considered to be merely a secondary result. 
Certain tentative and provisional suggestions are made (p. 493) re¬ 
garding the interpretation, upon the phyllode theory, of the significance of 
strands consisting exclusively of fibres, and also of the origin of the ‘ apical 
openings ’ occurring in the leaves of some submerged Monocotyledons. 
Anatomical evidence is then brought forward in favour of Henslow’s 
corollary to de Candolle’s theory (p. 488). It is shown, apparently for the first 
time, that the ‘ laminae’ of certain Pontederiaceae ( Eichhornia , Pontederia , 
Heteranther a) all agree in the presence of inverted as well as normal bundles. 
Inverted bundles are also recorded in the lamina of Sagittaria . Attention 
is drawn to Solereder’s discovery of inverted bundles in the ‘ laminae ’ of 
certain Hydrocharitaceae. It is recognized that Henslow’s corollary 
depends upon a more slender basis of evidence than the main theory, but 
the present writer is disposed to consider that it is well founded and that 
the blades of Monocotyledonous leaves are all, in reality, ‘ pseudo-laminae’. 
The systematic distribution of phyllodic anatomy among the Mono¬ 
cotyledons is then dealt with (p. 495), and it is shown that, as far as our 
present knowledge goes, it does not occur with any frequency outside the 
Helobiae, Liliiflorae, and Farinosae. On the theory of the origin of the 
Monocotyledons from the Ranalean plexus—which is accepted by the 
present writer—the Helobiae and Liliiflorae include those members of the 
Class which have departed least in character from the ancestral stock ; the 
Farinosae are probably not far distant from the Liliiflorae. In the case of 
the Spathiflorae, the only record relates to Acorus , which is probably 
the member of the Araceae retaining the most primitive floral characters 
—but this may be a mere coincidence. The Cohorts which rarely or never 
display phyllodic anatomy are those which, on other grounds, are regarded 
as advanced and highly modified. It is concluded that the systematic 
distribution harmonizes with the view that the type of anatomy here called 
‘ phyllodic ’ is an ancient character, revealing the petiolar origin of the 
Monocotyledonous leaf. 
