THE DISPERSAL OF SEEDS. 
109 
immersion in sea- water for more than a year, and that more than a 
century ago Linnjeus observed the tropical Entada scandens germinating 
on the coast of Norway. 
A more direct adaptation, however, is the imprisonment of air in 
structures surrounding the seed. The swamp-plants Carex amimllacea, 
C. vesicaria, and other species may well derive advantage from the 
balloon-like membranous utricle which surrounds their fruit. The white 
Water-lily (Castalia speciosa, Salisb.), which, by the bye, spread down- 
stream from a park near Banbury through the Chcrwell into the lower 
Thames, discharges its seeds in coherent lumps, rendered buoyant by the 
presence of air between the spongy aril and the testa of eacli seed. As 
the arils slowly decay, single seeds detach themselves from the lump and 
sink to the mud at the bottom. In the yellow Water-lily, however 
{Nymphcea lutca), there is no aril, but air bubbles are imprisoned within 
the slimy pericarp of the dehiscent berry-like fruit, and the seeds are 
liberated by its gradual decay. A somewhat smiilar air-filled cortex 
prevails in such well-known aquatics as Alisiiia, Sagittaria, Butonius, and 
Sparijan ium. More highly specialised are the fruits of the Cocoanut Palm 
{Cocos nucifera), the Double Cocoanut of the Seychelles {Lodoicea Sey- 
chellarum), and Nipa fruticans (Thunb.). In these cases the fruit has a 
membranous waxy epicarp, a fibrous mesocarp rendered buoyant by the 
presence of air between its fibres and a singularly dense and impervious 
endocarp. No instances speak more unmistakably as to the efficacy of 
these arrangements, for the Cocoanut is almost universal on the coasts of 
the scattered islands of the tropics ; the coco de mer " obtained that 
name from having been known as flotsam and jetsam before it was found 
growing ; whilst the much smaller Nipa is common in the brackish 
Sunderbunds of the East, floating for many miles in the waters of the 
Ganges and the Bay of Bengal without losing the power of germination, 
as its fossil ally Nipadites, now abundant in the London clay of Sheppey,. 
seems to have done in a tropical British sea in the remote Eocene past. 
When we turn to the adaptations to dispersal by the plant's own 
means we find far greater variety and complexity of contrivance, so that- 
I am at a loss to suggest any adequate classification of the cases. There^ 
is, I think, however, a decided progression from slight to more complete 
adaptation, and I feel inclined to place at the base of the series those 
cases of what has been termed — not very happily — "censer action," by 
which small-seeded capsular fruits practise an economy of seed by only 
opening partially and by the reaction to passing breezes or the brushing- 
contact of animals of their somewhat resilient peduncles. In the cap- 
sules of CaryophyllacccT, Primulacecne, Scrophulariacea?, Liliacea?, and 
Iridaceffi the seeds are unplumed, unwinged, and often large and heavy ;. 
but they are sometimes flattened, as in Tulipa and Iris, and the capsules 
open only upwards and in dry weather. The follicular fruits Del- 
phinium, Aconitum, Hcllehorus, &c., are similar, whilst the Poppy-head 
exhibits an additional refinement in the lids with which its pores are 
furnished. What is in effect only another case of this "catapult " or- 
"balistic " action, as it has been termed, is presented by many of the 
Compositte ; as, for instance, in the genus Centaurea, the Knapweeds. 
Here there is an erect rigid resilient peduncle, a common receptacle 
a 2 
