466 A NATURALIST IN THE PACIFIC CHAP. 



trunk dies and the primary branches supported by the aerial roots, 

 remain alive and in their turn give rise to secondary branches 

 similarly supported. 



(6) Although, as a rule, only one of the four ovules of 

 Rhizophora becomes a seed, occasionally a fruit contains more 

 than one seed. With R. mangle in Fiji about one per cent, of the 

 germinating fruits displayed more than one hypocotyl. 



(7) As a result of a protracted series of observations in Fiji, it 

 was established that in the case of a seedling of average length of 

 Rhizophora mangle a period of thirty-three weeks elapsed between 

 the date of fertilisation of the ovule and the detachment of the 

 seedling from the tree. In the instance of R. mucronata it was 

 placed at forty-two weeks. A period of thirty-eight weeks, or nine 

 to ten months, is regarded as typical for the genus. 



(8) It is established that normally there is no rest-period for 

 the seed in the case of Rhizophora, the seed at once beginning to 

 germinate on reaching maturity. In those exceptional instances, 

 however, where there is more than one seed, it is shown that in 

 some cases the seeds do not begin to germinate together, and that 

 a rest-period of at least some weeks can be at times postulated for 

 one of the seeds. 



(9) An analogy exists between the process of expulsion ending 

 in the detachment of the seedling of Rhizophora from the fruit and 

 the process of parturition. 



(10) Experiments show that Rhizophora seedlings can float 

 unharmed in sea-water for a period of at least three or four 

 months. Though nine-tenths or more float in sea-water, as much 

 as a fourth or a half sink in fresh-water. As a rule they float 

 vertically in fresh-water and horizontally in sea-water, the hori- 

 zontal position safe-guarding the plumule against the risk of being 

 withered up by the sun in a calm sea. 



(n) It is shown that in the case of Bruguiera rheedii the 

 seedlings when detached from the tree can float unharmed in 

 sea-water for months. In their specific weight they display a 

 similar fine adjustment to the density of sea-water, as is above 

 described in the case of Rhizophora. 



(12) With this species of Bruguiera, fertilisation takes place 

 not in the unopened flower, as in Rhizophora, but after the flower's 

 expansion ; and a very singular mechanism is here described which 

 secures the completion of the process. 



(13) A period of twenty-seven weeks elapses between the 

 fecundation of the ovule and the detachment of the seedling from 



