xx THE GERMINATION OF FLOATING SEEDS 87 



Summary of the Chapter. 



(a) The tendency of the floating seed or fruit to germinate in 

 the brackish water of tropical estuaries is especially characteristic 

 of the plants of the mangrove-swamp and their vicinity ; but with 

 those of the beach trees that occur in the river-drift it is rarely if at 

 all to be observed. 



(6) From the wide distribution of plants of the mangrove- 

 formation it is evident that this readiness of the floating seed or 

 fruit to germinate is not prejudicial to the dispersal of the species. 



(c) It may perhaps be in the main attributed to a strain of 

 vivipary running through all the plants of the mangrove-formation, 

 which finds its extreme development in the viviparous species, 

 where germination takes place on the tree. But it is probably 

 favoured by the superheating of the waters of tropical estuaries. 



(d) In the case of the buoyant seeds of several climbers and 

 creepers of the Leguminosae and Convolvulaceae, more or less 

 littoral in their station, it is shown that in warm water, whether 

 fresh or salt, a good proportion are apt to sink through incipient 

 germination, which results when the experiment is made in sea- 

 water in the death of the embryo. 



(e) Though in tropical currents of ordinary temperature a good 

 number of such floating seeds would escape this risk, it is argued 

 that there are certain warm areas in the tropical seas that would 

 prove much more fatal to the chances of these drifting Leguminous 

 and Convolvulaceous seeds than the icy waters of a polar current. 

 It is thus held that these seeds often sink in mid-ocean in tropical 

 latitudes through abortive germination. 



(/) The study of the behaviour of the floating seed or fruit 

 leads us to the borderland of vivipary. In the scale of the 

 germinative capacity of plants it is possible to arrange a con- 

 tinuous series that commencing with the mangroves, where germi- 

 nation takes place on the tree, ends with those numerous inland 

 plants where seeds are liberated in an immature condition. 



(g) It is suggested that the viviparous habit may have been the 

 rule under the uniform climatic conditions of early geological 

 periods and that with the differentiation of climates that marked 

 the emergence and extension of the continental areas the viviparous 

 habit has been lost, except in those regions of the mangrove- 

 swamps which to some extent retain the climatic conditions once 

 general over the globe. With differentiation of climate the true 

 seed-stage with its varying rest-periods has been developed. 



