Chap. IV] TROPICAL DISTRICTS CONSTANTLY MOIST 335 



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

 W'icsncr ah-cady referred to. 

 The admirable researches of Raciborsl<i regarding W^^ structure of Jlo'Mcr- 

 :,Is 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 bj' him in a few cases only. Yet the peculiar 

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

 their calyx until sliortly before their antliesis, 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 Rihai (Fig. 178) and Heliconia 

 caribaea always full of rain-water ; the 

 flower-buds were below water-level, but 



shortly before opening they raised ^ , ^'*N^ 



themselves above it by curving sharply. a^^'^ ■Aiil '^^'^-^ 



In like manner, in Nidularium (Fig. 

 i6f,) 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, whicli accumulates in the 

 sac-like fused pairs of bracts surround- 



., fl , 1 r ._ ■ A I'lG- 1/7- ManLrifer.i indica. End of twig. 



Ulg the flower-buds of certam Acan- ^he young le.ives flaccidly pendent. Half 



thaceae (Fig. 1 79), which are so tensely 'lie natural size. After Stahl. 

 filled that a puncture causes the liquid 



to spurt out violcntl}^ 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 

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

 especially as regards secreting hydathodes. The number of species with 

 '.vater-holding calyces is small — so far as is known only thirteen species, 

 limited to representatives of the families of Bignoniaceae, Solanaceae, 

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

 water-holding bracts are very common. 



