First Group.—The floating power is derived from unoccupied space in the cavity of the seed or fruit, no part of the seed or fruit as a rule possessing independent floating power.
Sub-group I., where the seed is concerned.
Section I. The seeds have little or no albumen, and neither the tests nor the seed-contents have any buoyancy. The cotyledons are generally large, foliaceous, and crumpled or folded, or otherwise arranged, so that the seed-cavity is incompletely filled.
- S. G. Hibiscus tiliaceus.
- G. Hibiscus diversifolius.
- S. G. Thespesia populnea.
- S. Suriana maritima.
- G. Kleinhovia hospita, variable.
- S. G. Colubrina asiatica.
- S. Dodonæa viscosa.
- G. Argyreia tiliæfolia, variable.
- G. Ipomœa bona nox, variable.
- G. Ipomœa glaberrima, Boj.
- S. G. Ipomœa grandiflora.
- S. G. Ipomœa pes capræ.
- G. Ipomœa turpethum, variable.
- G. Cassytha filiformis.
- S. Euphorbia atoto.
Notes.—The species marked “variable” have seeds that sometimes sink and sometimes float. With the exception of Kleinhovia they are only at times littoral in station.
The plants of the British flora are represented by Convolvulus soldanella and C. sepium, the last being “variable” and not a littoral species.
Section II. All the seeds belong to the Leguminosæ. Neither the tests nor the seed-contents have any buoyancy, the floating power arising from a large central cavity produced by the bending outward of the cotyledons during the final shrinking stage of the maturation of the seed.
- S. Mucuna (generically).
- G. Mucuna urens D.C. (Hawaii).
- G. Mucuna, species of.
- S. G. Vigna lutea.
- S. G. Cæsalpinia bonducella.
- G. Cæsalpinia bonduc.
- G. Entada scandens.
Sub-group II., where the fruit is concerned.
Section III. The seed only partially fills the fruit-cavity, and as a rule is not buoyant. The fruit shell, usually woody, may be also buoyant.