through Self-adaptation to a Moist or Aquatic Habit . 727 
The development of the lower cotyledon only is probably analogous to 
the well-known fact that of two opposite leaves growing on a horizontal 
branch the lower will be larger than the upper. This is said to be due to 
gravity ; but as the larger leaf requires the most water, it must be upon 
that which gravity acts. If the bough be kept reversed, then the leaves 
which would have been naturally uppermost, becoming the lower, now grow 
to be the larger. 1 
10. Monocotyledonous Dicotyledons. 
In addition to the plants mentioned in my previous paper, Corydalis 
solida may be considered, for although Sir J. D. Hooker, in his Student’s 
Flora, regards it as having connate cotyledons, M. Velenovsky considers it 
to have one ; and he discovered an additional coincidence with Mono¬ 
cotyledons. It consisted in a peculiar adaptation of the hypocotyl and the 
petiole of the cotyledon, in that these are covered with absorbing hairs and 
can give rise to endogenous adventitious roots, so that the petiole acts as 
a true root. 
This is not an isolated fact, for M. Gatin had previously observed that 
among certain Monocotyledons the petiole and cotyledonary sheath are 
sometimes covered with absorbing hairs, as e.g. in Trachycarpus Martiana 
and Strelitzia. 2 
It may also be noted that Corydalis solida has a conn and glabrous 
dissected foliage ; the former may perhaps primitively have been for storage 
of water and the leaf submerged. In Ranunculus Ficaria and Carum 
Bulbocastanum the embryo is greatly arrested in the ripe seed ; so that 
germination in both alike is very slow, features due to degeneracy which 
water can account for. 
Miss Sargant, quoting from Hegelmaier’s observations, shows that the 
development of the cotyledon is in a crescent-shaped ridge which thus agrees 
with the Water-lily, thereby acquiring a sheathing base. ‘ Hegelmaier and 
Schmid consider one possibility only—the formation of a single cotyledon 
from the original pair by suppression of the second.’ 3 Miss Sargant also 
refers to Corydalis cava , as having an ‘ embryo monocotyledonous from the 
first. . . . From the researches of Dr. Schmid, we know that no traces of the 
194 (p. 155) ; Fig. 462 (p. 429) ; quoted from The Embryo of Ceratozamia by H. A. Dorety. Bot. 
Gaz. xlv, 1908, pp. 412-16, Figs. 1-7. 
1 Influence des agents exterieurs sur l’organisation polaire et dorsiventrale des plantes, par 
M. L. Kolderup Rosenvinge. Rev. Gen. de Bot., vol. i, Figs. 12, 13, p. 131. See Author’s experi¬ 
ments, Origin of Plant Structures, p. 205. 
2 La morphologie de la germination et ses rapports avec l’anatcmie, par M. C. L. Gatin* 
Rev. Gen. de Bot., xx, p. 273. 
3 The Reconstruction of a Race of Primitive Angiosperms. Ann. Bot., vol. xxii, p. 157. 
