462 A NATURALIST IN THE PACIFIC chap. 



whilst the fruits contain the cotyledons at the bottom of the seed- 

 cavity. 



As with Rhizophora, there is a rather curious adjustment of the 

 buoyancy of the seedling to the density of sea-water. About 

 75 per cent, of those afloat in the fresh-water of rivers assume the 

 vertical position, the plumular end protruding between two and five 

 lines (5 to 12 mm.) above the surface, while the remainder float 

 horizontally or nearly so. In sea-water about 50 per cent, float 

 either vertically or steeply inclined, and the other half float 

 horizontally. 



With regard to the times of flowering and fruiting, it may be 

 remarked that the trees are mostly in flower during the hot months 

 from November to February, and that the fruiting is in active 

 operation in the latter half of March. The floating seedlings occur 

 in abundance in the river-drift at the end of the year, a circum- 

 stance which corresponds with the fact that a period of six months 

 passes between the fertilisation of the ovule and the fall of the 

 seedling into the water. 



Fertilisation, or, more correctly speaking, the discharge of the 

 pollen, takes place after the opening of the flower, and not before, 

 as in the case of the species of Rhizophora. The flower-bud is 

 at first erect, but subsequently it begins to bend downwards, and 

 ultimately it hangs more or less vertically. The provision to secure 

 fertilisation under these circumstances is rather curious. Without 

 some such contrivance as is below described, the pollen would 

 merely fall out of the flower. Each petal has its sides rolled or 

 folded inwards so as to completely inclose two stamens. In the 

 bud the folded petals are white and flexible, but as the flower 

 expands they redden and become dry and elastic, and are only 

 prevented from flying open with a spring by the interlocking of the 

 hairy tips of their lobes. Whilst the folded petals are becoming 

 stiff and elastic during the opening of the flower, the inclosed 

 stamens are at the same time preparing themselves for their 

 function. The anthers are dehiscing and the filaments are acquiring 

 elasticity. All is now ready, and a slight shake or a touch puts the 

 mechanism into action. The petals unfold themselves with a spring, 

 and the stamens thus suddenly exposed and released fly forward, 

 and a little shower of pollen is thrown towards the centre of the 

 flower. This process is accomplished in ordinary fine weather 

 during the first twenty-four or thirty-six hours after the expansion 

 of the flower. When the opening occurs in the early morning, 

 half of the stamens will be found released in the evening and the 



