Willis.—The Origin of the Tristichaceae and Podostemaceae. 301 
In the first place, to consider the possibilities of their having been 
water plants at all, there are several facts which are opposed to this 
hypothesis. To begin with, their seeds, with one or two exceptions among 
the most modified species of the orders, but with none among the more 
primitive, are all alike—very numerous, minute, exalbuminous, with an 
outer coat of cells which become mucilaginous on wetting, and contained in 
capsules which open only in dry air. These seeds are singularly ill adapted 
to the mode of life which characterizes these families. They fall upon the 
dry naked rocks within a few days of the beginning of the dry season, which 
in most of the districts where these families grow lasts for several weeks. 
Before the end of it the enormous majority will have blown away, and once 
off the rocks their chance of reaching suitable spots for growth is practically 
nil. But a few remain, and when the water rises, the bulk of these will wash 
away. In the case of plants of Hydrobryum olivaceum or Lawia zeylanica , 
which I estimated to bear (where well grown) from 20,000 to 30,000 seeds 
on an average, the number of seedlings—-or rejuvenescences—which may 
arise is rarely more than two or three, sometimes as many as ten, often 
enough one or even none. Were it not for rejuvenescence of the old thallus, 
one gathers the impression that the survival of some of the highly modified 
species like these would be problematical. 
But even when they have actually germinated, many of the seedlings 
are washed away, and I do not think that it is much exaggeration to say 
that six weeks after germination each parent plant is usually represented by 
not more than one or two young ones. 
But now, as these ill-adapted seeds are found throughout the families, 
except in a very few of the most modified species, it cannot be a stretch of 
probability to suppose that they are a legacy from the common ancestor, 
which consequently must in all reasonable probability have been a land 
plant. 
Further, as the . loss of seed is so tremendous, and all these plants 
set great numbers, it is evident that the original ancestors must have been 
plants which set seed freely and in great quantity, otherwise they could 
scarcely have adopted this mode of life. Now, as is well known, this 
is a character just the reverse of what is usually found in the plants of 
quieter water, and is therefore another argument in favour of the ancestor 
having been a land plant. 
Again, assuming the ancestor to have been a water plant, it is evident 
that unless the seeds arrived at the rapids in large numbers, sufficient 
to allow of the enormous destruction that goes on, the chance of any 
modification appearing to suit the progeny to the new mode of life would be 
all but absolutely zero. And this is just what one cannot imagine happen¬ 
ing. The only means of carriage to a distance that the seeds possess is to 
adhere to the feet of wading birds that have just been in the water, and are 
