5., 6. Dioclea (violacea?), from Fiji (natural size). Here the kernel (b) is buoyant and endows the seed with floating power. Though the shell (a) possesses a thick layer of reddish-brown cellular tissue, this tissue contains but little air and aids the floating power but slightly (see page [113]).
7. Strongylodon lucidum, from Fiji (natural size). The floating power is due entirely to the buoyant kernel (b). There is a very scanty amount of loose brown tissue (a) under the raphe; but it has no appreciable effect on the buoyancy (see page [113]).
8., 9., 10. Cæsalpinia bonducella and C. bonduc, from Fiji (natural size). Neither the seed-tests (a) nor the kernel (b) have any floating power in themselves, the buoyancy being connected with a large internal cavity (c), which normally is intercotyledonary, as in Fig. 8 (C. bonducella). With both plants, but more especially with C. bonduc (Figs. 9 and 10), there may be a lateral cavity (d), or the kernel may be loose in the shell (Fig. 10), but this does not necessarily imply buoyancy (see page [194]).
11., 12. Arenaria peploides (enlarged: seeds 4 mm. in size). Here the curved embryo (a) sinks, and the spongy air-bearing albumen (b) gives buoyancy to the seed (see page [116]).
13. Euphorbia paralias (enlarged: seeds 3 mm. in size). The kernel (b) sinks, and the seed owes its buoyancy to a layer of air-bearing tissue (a) in the shell (see page [116]).
14. Morinda citrifolia (enlarged pyrene 7 mm. long). The floating power is due to the bladder-like air cavity (a). The seed (b) proper is enclosed in the woody tissue behind the bladder (see page [112]).
15. Cucurbita (seed enlarged), from the Valparaiso beach-drift (see page [125]). The kernel (b) has no buoyancy. The shell (a) is formed of two layers of air-bearing tissue, the outer composed of prismatic cells and the inner of a spongy vacuola-material.
[To face page [111].
Diagrams illustrating some of the causes of seed-buoyancy.