EXPLANATION OF THE DIAGRAMS ILLUSTRATING 

 THE CAUSES OF SEED-BUOYANCY 



i. Entada scandens (natural size) : (<?), the shell ; (b), the kernel ; (<), the inter- 

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

 hard chilinous coat, and an intermediate layer of brown cellular tissue 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 power (see page 1S1). 



2. Miii una urens, from Hawaii (natural size). The kernel (6) sinks, and the shell has 



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

 brown, air-bearing, spongy tissue {a). This, however, is not sufficiently developed 

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

 (see page ill). 



f Murima gigantea, from Fiji (natural size). The kernel (/<) sinks, and the seed owes 



3. its floating power entirely to the existence in the shell (a) of a layer of brown, 



4. 1 s P on gy> air-bearing tissue which is mostly developed at the circumference and is 



almost wanting at the flat sides of the seed (see page 115). 



' Dioclea (violacea?), from Fiji (natural size). Here the kernel (6) is buoyant and 



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

 g. J layer of reddish-brown cellular tissue, this tissue contains but little air and aids 



( the floating power but slightly (see page 1 13). 



7. Strongylodou hicidum, from Fiji (natural size). The floating power is due entirely 



to the buoyant kernel (/'). There is a very scanty amount of loose brown tissue 

 (<7) under the raphe ; but it has no appreciable effect on the buoyancy (see 

 page 113). 



tcsalpinia bonducella and C. bonduc, from Fiji (natural size). Neither the seed- 

 tests (a) nor the kernel (/>) have any floating power in themselves, the buoyancy 



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

 9.-, donary, as in Fig. 8 (C. bonducella). With both plants, but more especially 



10. with C. bonduc (Figs. 9 and 10), there may be a lateral cavity (</), or the kernel 



may be loose in the shell (Fig. 10), but this docs not necessarily imply buoyancy 

 \ (see page 194). 



(Arenaria peploiJes (enlarged : seeds 4 mm. in size). Here the curved embryo (a) 

 sinks, and the spongy air-bearing albumen (/>) gives buoyancy to the seed (see 

 I2- ^ P a S e IJ 6)- 



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 nim. 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 1 12). 



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. 



