4i9 
Geophilous Species of Peperomia. 
shaped cotyledon in P .parvifolia (Fig. 22, PL XXIX). A hypocotyledonary 
bulb is formed in due course, and the structure of the young plant then 
consists, as in Peperomia , of the primary root, the bulb, and two opposite 
leaves with an undeveloped plumule (Text-fig. 2, p. 418). 
Further it is of interest to notice that a median longitudinal section 
through the young seedling shows the two leaf-traces, from the ‘cotyledon * 
and from the ‘ first leaf,’ meeting below the plumule at the same horizontal 
level, and fusing together to form the central cylinder of the bulb and root 
(Text-fig. 4, p. 418). 
A transverse section of a young seedling of Arum maculatum i in the 
neighbourhood of the stem-apex, shows that the midrib of the cotyledon 
and the midrib of the first leaf are directly opposite to one another, whilst 
later leaves depart from this arrangement 1 , and have a very different 
phyllotaxy (Text-fig. 3, p. 418). 
An analogous case;, though still more specialized, seems to be afforded 
by Tamus communis 2 . The cotyledon has lost almost all trace of its leafy 
characteristics, but the first leaf, which is the only green leaf of the first 
year, is rapidly developed, as in Arisaema , and is directly opposite to the 
absorbent cotyledon. Similar external similarity in the mode of germina- 
tion is shown by Liliaceae and allied geophilous Monocotyledons. From 
the foregoing considerations it seems not improbable that the absorbent 
cotyledon of at least some Monocotyledons is homologous with the modified 
absorbent cotyledon of these Peperomias, whilst the homologue of their 
aerial green cotyledon is to be found in the so-called ‘first leaf’ of the 
monocotyledonous seedling (Figs. 49 and 50, PI. XXX). 
The Origin of Monocotyledons. 
In putting forward these views of the possible origin of Mono- 
cotyledons from a dicotyledonous ancestry, suggested by the discovery of 
the seedlings of these geophilous Peperomias, I find myself in opposition 
to Miss Sargant’s well-known theory 3 of the origin of Monocotyledons 
from a dicotyledonous stock, deduced from the anatomical study of their 
seedlings. According to her theory the single cotyledon of Monocotyledons 
is due to the fusion of the two cotyledons of the ancestral Dicotyledon, 
whilst in this paper evidence has been brought forward to show that 
the monocotyledonous habit may have been acquired by the adaptation 
of the two cotyledons of the ancestral Dicotyledon to different functions. 
Very little in the way of anatomical evidence has been adduced to 
1 Scott and Sargant, Development of Arum maculatum , Ann. Bot., xii, p. 407, PI. XXV, 
Figs. 11-14. 
2 Gardiner and Hill, A. W., Proc. Camb. Phil. Soc., xi, p. 445, PI. V, Figs. 3-7. 
3 Sargant, Ann. Bot., vol. xvii, p. 1. 
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