370 Hems ley. — On a Drift-seed 
plants in the tropics, and frequently spring up from seeds that 
have floated hither and thither on the sea, and finally been 
cast ashore to fulfil their destiny. Indeed, it is not essentially 
a shore-plant, but rather a climber of lofty trees ; yet its seeds 
are not uncommonly met with in the drift of the Caribbean 
Sea, and they are sometimes carried far up into the north 
Atlantic by the Mexican Gulf stream. This is one of the 
points of interest attaching to it to be discussed here ; another 
is the dimorphic or trimorphic development of the seeds. The 
latter phenomenon may be described first. Normally there 
are four seeds closely appressed and forming together a 
spheroid, each seed having two vertical facets and a convex 
back. Sometimes only two or three seeds are developed, and 
they are correspondingly different in shape ; and not unfre- 
quently only one is formed. When the latter is the case, the 
one seed assumes the size and nearly the shape of the four 
seeds combined, differing in being more depressed. It is also 
slightly furrowed at right angles into four quarters, resembling 
the four seeds ; and the basal hilum is very large and oblong 
in outline. The furrows probably correspond to the septa of 
the ovary, which disappear at an early stage of the develop- 
ment of the seed or seeds. Instances of the abortion of some 
of the ovules and similar adaptations of the developed seed or 
seeds to the size and shape of the seed-vessel are probably 
not uncommon ; and, as Mr. C. B. Clarke reminds me, some 
of the Commelinaceae exhibit this peculiarity to an equally 
remarkable degree with Ipomoea tuberosa. 
As already stated, some of the species of Ipomoea are 
among the commonest of seaside plants in the tropics, and 
from actual observation it is known that their seeds will bear 
long immersion in salt water, or rather float on it, without 
losing their germinating power. Further, it has been ascer- 
tained that the seeds often germinate after being cast ashore. 
Ipomoea pes-caprae is a notable example, being found on sandy 
shores, including the most remote islets, throughout the warmer 
zone. Their seeds are well adapted for long journeys by water, 
having a dense, almost crustaceous testa, which protects the 
