10, 



II. 



12. 



EXPLANATION OF THE DIAGRAMS ILLUSTRATING 

 THE CAUSES OF SEED-BUOYANCY 



I. Entada scandens (natural size): (a), the shell; {b), the kernel; (c), the inter- 

 cotyledonary cavity. The shell consists of three coats — an outer and an inner 

 hard chitinous coat, and an intermediate layer of brown cellular tis.sue contain- 

 ing little or no air. The buoyancy is due entirely to the central cavity, neither 

 the seed-tests nor the seed contents possessing any floating povi^er (see page i8i). 



2 Mucuita iireus, from Hawaii (natural size). The kernel (b) sinks, and the shell has 

 no floating power except where it possesses (under the raphe) a layer of dark 

 brown, air-bearing, spongy tissue (^). This, however, is not sufficiently developed 

 to endow the seed with buoyancy, which is due to the intercotyledonary cavity [c). 

 (see page iii). 



' Muruna }^ii;aiUen, from Fiji (natural size). The kernel (/;) sinks, and the seed owes 

 its floating power entirely to the existence in the shell [a] of a layer of brown, 

 spongy, air-bearing tissue which is mostly developed at the circumference and is 

 almost wanting at the fl^t sides of the seed (see page 115). 



Dioclea (vioiacea ?), from Fiji (natural size). Here the kernel {b) is buoyant and 



5. I endows the seed with floating power. Though the shell {a) possesses a thick 



6. 1 layer of reddish-brown cellular tissue, this ti.ssue contains but little air and aids 

 the floating power but slightly (see page 113). 



Strongylodon lucidum, from Fiji (natural size). The floating power is due entirely 

 to the buoyant kernel [h). 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). 



(Ciesalpinia bonducella and C. hondiic, from Fiji (natural size). Neither the seed- 

 tests (rt) nor the kernel [b] have any floating power in themselves, the buoyancy 

 being connected with a large internal cavity (c), which normally is intercotyle- 

 9. { donarv, 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). 

 Arenaria feploulcs (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 ciirifolia (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. Cuciirbita (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. 



