2 95 
Evolution of Monocotyledons. 
the embryo-sac. The case of such psuedomonocotyledons as 
Ranunculus Ficaria, 1 Corydalis cava and Carum Bulhocastanum 
illustrates this point. Resort is therefore made to the evidence of 
comparative seedling anatomy. 
Very generally, in the seed-leaf of Monocotyledons, a true 
midrib is replaced by two equal bundles. In some forms these 
bundles are so arranged as to suggest that each represents the midrib 
of an ancestral cotyledon, and a comparison of certain monocotyle- 
donous seedlings, such as Anemarrhena, with those of some Ranalean 
forms (for example, Eranthis hiemalis) supports this suggestion (58, p. 
109 ; PI. II). The Anemarrhena seedling anatomy may be taken as 
a primitive type, since it leads by intermediate forms through at least 
four lines within the Liliaceae. It may be described shortly as follows 
(57, 58, p. 109; PI. II, figs 1-6):— 
The cotyledon of an Anemarrhena seedling is somewhat 
flattened, and the plumule is rather late in development. In the 
example figured by Miss Sargant, it is still completely enclosed 
within the base of the cotyledon. The axis, which is somewhat 
thickened immediately below the plumule, passes at once into the 
strongly developed primary root. The vascular system of this 
seedling is symmetrical, two large bundles running the whole length 
of the cotyledon, which is elliptical in transverse section. Towards 
the base of the cotyledon, the two bundles are slightly displaced 
from their hitherto symmetrical position by the formation and 
growth of the plumule; but although this displacement extends into 
the transition region, the transition itself takes place in a symme¬ 
trical manner. Three branches of protoxylem are derived from each 
xylem group, and each phloem group divides into two. The lateral 
branches of protoxylem fuse in pairs, and the result is a tetrarch 
root-stele. 
In certain Dicotyledons, the seed-leaves are normally united to 
a greater or less degree, sometimes by one margin only, but more 
often by both. In the latter case the united petioles form a tube, 
sometimes of considerable length (see Sargant, 59; Table I, pp.73,74). 
Petiolar tubes of this kind are found in a good many of the 
Ranunculaceae and in other orders ; and in all investigated cases, 
they are accompanied by a much shortened and thickened hypocotyl. 
1 In this species the evidence from embryogeny has led Sterckx (66) to 
assume that inonocotyly has arisen by fusion of two cotyledons; Hegelmaier 
(29) and .Schmid (63), on the contrary, think that suppression of one cotyle¬ 
don has taken place 
