342 BOTANICAL GAZETTE [MAY 
occur frequently among geophytes and to be useful to the plant 
growing under conditions which determine the geophilous habit. 
They are therefore in all probability adaptations to that habit. 
Two more—the stem-anatomy and the apparently terminal coty- 
ledon in the embryo—may be considered as direct consequences 
of such adaptations ; the stem anatomy acquiring its peculiar feat- 
ures from the insertions of numerous broad-based leaves on a 
squat subterranean axis,and the embryonic cotyledonary member 
arising from the congenital fusion of two ancestral cotyledons. 
The seventh character—trimerous floral symmetry—bears no 
obvious relation to the geophilous habit, but is not inconsistent 
with it. 
In a paper read before the Linnaean Society in 1892, Mr. 
Henslow* maintains that monocotyledons were derived from 
dicotyledons by an adaptation to an aquatic habit. He bases his 
argument on the large proportion of monocotyledons which 
are aquatic, and on the nature of the characters, external and 
internal, which distinguish them from dicotyledons. These are 
on the whole, he suggests, the characters of water plants. He 
considers the single cotyledon as representing one of the dico- 
tyledonous pair, the other having disappeared. 
Other botanists have suggested the derivation of monocoty- 
ledons from an aquatic or amphibious ancestor. Some of their 
characters would bear this interpretation, and indeed aquatic 
plants have several features in common with geophytes. The 
main axis of the great majority of water plants is hidden in the 
mud of the river or lake bed, and the green parts in the colder 
climates die down on the approach of winter. The subterranean 
stem is commonly a rhizome, but it bears upright buds. When 
broad-based leaves are inserted on the shortened axis of such a 
bud, their traces might naturally be arranged in the scattered 
fashion actually found among the Nymphaeaceae (Henslow, / ¢ 
p. 512) and monocotyledons, But, on the other hand, the 
tendency of an aquatic habit is to reduce the vascular tissue 
altogether; the leaf traces weed wos pea pee and the vascu- 
26 HENSLow, G., A theoretical 1 exogens by self-adaptation 
to an aquatic habit. Linn. Soc. Sete 29: 485. 1892. 
