300 Willis.—The Origin of the Tristichciceae and Podostemaceae . 
ripen and are shed on the rocks, where they germinate with the rise of 
water at the beginning of the rains. The original plants usually die, but 
may rejuvenesce if there be an early rise of water. 
To go on now to the question of the origin of these plants in the first 
place, what is their origin regarded merely as Angiosperms, which they 
undoubtedly are ? Have they, as some writers think, descended continuously 
in water from aquatic pre-Angiosperms, or have they sprung from the 
general tree of the Angiosperms, which it is generally conceded began upon 
land ? I think that there can be no doubt that the latter supposition 
is correct. If they were an independent survival of pre-angiospermous water 
plants, one would expect to find their embryology very different from what 
it actually is, for, as Warming, 1 Went, 2 and Magnus 3 have shown, it is 
typically dicotyledonous. I think that on this ground alone they must 
be regarded as descendants of the general tree of the Dicotyledons. 
If for the first time one saw any of their flowers without knowing from 
what sort of plant they came, one would never for a moment imagine them 
to be the flowers of water plants. They are typical simple mono- or 
a-chlamydeous dicotyledonous flowers, sometimes ento-. sometimes anemo- 
philous, and always, unless they happen to be cleistogamic, awaiting the fall 
of the water-level to expand in the air on the dry rocks, and be pollinated 
there. They do not look in the least like the flowers that one would expect 
in plants with a long line of hydrophytic ancestry, leading back to ante- 
floriferous days. 
The fruit again is typically a land fruit. Only in the most highly 
modified species of the whole family— Farmeria metzgerioides —does it show 
any special suitability to the peculiar aquatic mode of life of these plants. 
Never, one would imagine, would a primitively aquatic family possess 
minute seeds in a capsule that only dehisced in dry air. Never would those 
seeds possess an outer layer of cells that became mucilaginous on wetting. 4 
Nor would the seedlings be so badly provided with holdfasts that they were 
constantly washed away. There is no disputing the evidence that these 
peculiar families are the descendants of other Dicotyledons, and of Dicotyle¬ 
dons that lived on land, even if their immediate ancestors were water plants. 
The next question is, Where did their immediate ancestors live ? Was 
it (i) on land or (2) in water, and in the latter case were they water plants 
(a) of the reaches between the rapids and waterfalls in which the Tristicha- 
ceae and Podostemaceae live; (b) of moving water of the rivers of the 
plains or low country; or (c) of ponds or marshes ? 
1 Warming: Familien Podostemaceae II. Kgl. Dansk. Vidensk. Selsk. Skr., 6 Raekke, ii, 
1882. 
2 Went: Unt. liber Podostemaceae. Verh. Koninkl. Akad. Amsterdam, xvi, 1910. 
8 Magnus: Die atypische Embryonalentvv. d. Podostemaceen. Flora, cv, 1913, p. 275. 
4 This has often been described as an adaptation for clinging to the rock, by people who have 
forgotten that with another rise of water the seeds once more become loose and are washed away. 
