Chap. IV] TROPICAL DISTRICTS CONSTANTLY MOIST 335 



statements regarding this subject occur in the works of Potter, Stahl, and 

 Wiesner already referred to. 



The admirable researches of Raciborski regarding the structure ofjloiver- 

 buds were conducted partly on tropical plants. Characteristic distinctions 

 depending on climate between the flower-buds of tropical plants and plants 

 of other zones were mentioned by him in a few cases only. Yet the peculiar 

 phenomenon, that flower-buds arc immersed in water, or contain water in 

 their calyx until shortly before their authesis, appears to be limited to humid 

 tropical districts. For instance, in the West Indies I found the boat- 

 shaped bracts in the inflorescence of 

 Heliconia Bihai (Fig. 1 78) and Heliconia 

 caribaea always full of rain-water ; the 

 flower-buds were below water-level, but 

 shortly before opening they raised 

 themselves above it by curving sharply. 

 In like manner, in Nidularium (Fig. 

 165) I saw the short inflorescence 

 nestling between the bracts always 

 submerged in a cistern supplied with 

 rain and dew, out of which the open 

 flowers protruded singly. The boat- 

 like bracts of the long distichous in- 

 florescence of species of Vriesea, for 

 instance Vriesea incurvata, contain a 

 mucilaginous liquid, which completely 

 surrounds the bud and is probably 

 secreted by the plant. The latter is 

 certainly true of the similar mucila- 

 ginous liquid, which accumulates in the 

 sac-like fused pairs of bracts surround- 

 ing the flower-buds of certain Acan- 

 thaceac (Fig. 179), which are so tensely 

 filled that a puncture causes the liquid 



to spurt out violently. Flower-buds with a water-holding calyx were first 

 described by Treub in connexion with Spathodea campanulata, and have 

 formed the subject of a comprehensive and conclusive monograph by 

 Koordcrs which has brought to light a number of interesting details, 

 especially as regards secreting hydathodes. The number of species with 

 water-holding calyces is small — so far as is known only thirteen species, 

 limited to representatives of the families of Bignoniaceae, Solanaceae, 

 Verbenaceae (Fig. 180), Scrophulariaceae, and Zingiberaceae — whereas 

 water-holding bracts are very common. 



Fig. 177. Mangifera indica. End of twig. 

 The yonng leaves flaccidly pendent. Half 

 the natural size. After Stahl. 



