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._ [Illustration: Diagrams illustrating some of the causes of seed-buoyancy.]