through Self-adaptation to a Moist or Aquatic Habit. 737 
leaf-blade of a Dicotyledon. Conversely, a submerged leaf of any aquatic 
plant of this class rarely, if ever, agrees with a Monocotyledon. Thus the 
ribbon-like form of Lobelia Dortmanna 1 and others has really a midrib 
with lateral ribs branching from it at the base. They subsequently run 
parallel, imitating , but are not identical with, say, those of a grass blade or 
Sagittaria. Hippnris has a single midrib without lateral ones, and thus is 
degraded to a very simple condition. 
Could, therefore, Monocotyledons have arisen so early as to have 
preceded the reticulated venation of Dicotyledons ? The earliest kind of 
branching venation appears to have been dichotomous, as seen in Ferns 
(Adiantum ) and the Ginkgo of to-day; but in Cordaites laevis , as figured 
by Dr. Scott 2 after Renault, the leaf is represented of the simplest kind 
with parallel venation. 
Something of that sort, perhaps, supplied the original type of leaf of 
Monocotyledons, now represented by the petiole only. This, however, 
professes to be no more than guess-work and a suggestion only. At all 
events, as Miss Sargant notes, the cotyledons of Monocotyledons would 
seem to carry the two strands, one being the relic of a lost cotyledon, with 
no third strand in the place of a true midrib as in Dicotyledons. In some 
cases, as Eucomis nana , according to her description, the two cotyledonary 
strands approach so as to make a pseudo-midrib ‘ exactly opposite to the 
first leaf’. 3 It also occurs, she adds, in Lilium and Allium. 
15. Reproductive Organs. 
In the section with this heading 4 I omitted to allude to the degraded 
flowers of some aquatic Dicotyledons. Thus the Halorageae, apparently 
derived from Onagraceae, exhibit several instances of aquatic genera having 
much reduced flowers, both in size and number of parts, such as in wanting 
a corolla and being unisexual. Elatineae, again, affords another instance. 
Hydrocotyle has no vittae, in accordance with the well-known fact that 
oils and resins are much reduced or absent from plants growing in moist 
regions. 
Similarly the degradations of the flowers of Grasses, Sedges, Lemna , 
Zoster a, and many others are very obvious. On the other hand, as long as 
the flowers of aquatic plants are visited by insects, there is no reason why 
they should not resist degeneration in size and attractiveness or number of 
parts, as is the case in Nymphaeaceae, &c.; though in the Water-crowfoots 
the flowers are, mostly, considerably degraded. 5 
1 Bentham spells this Dortmanni ; Hooker, Dortmanna . L. is the authority for both. 
2 Studies in Fossil Botany, p. 522. 
3 Theory of the Origin of Monocots., etc. Ann. of Bot., vol. xvii, p. 19 ; cp. PI. I, Fig. 6. 
4 loc. cit., p. 524. 
6 See my paper on the Self-fertilisation of Plants, Trans. Lin. Soc., Sec. Ser.—Bot., i, p. 347. 
