ix THE GERMINATION OF FLOATING SEEDS 85 



may have been often impossible, since the seeds that did not begin 

 to germinate on the plants of the swamps would probably do so* 

 in the tepid water of the sea. Viviparous plants would, however,, 

 be placed at no greater disadvantage than they are at present, since- 

 the genera Rhizophora, Avicennia, and others are now only 

 dispersed by the floating seedlings. But such an increase of 

 temperature at the present time would mean the death in the 

 current of the floating seeds and fruits of nearly all non-viviparous 

 shore-plants. As a rule every Leguminous and Convolvulaceous 

 seed would swell up and go to the bottom ; whilst fruits like those 

 of Barringtonia racemosa and Carapa obovata, that often germi- 

 nate afloat in tropical estuaries, would invariably do so under the 

 changed conditions, and the seedlings not being adapted for ocean 

 transport would perish. 



Yet we know that with the seeds of many inland plants 

 temperature has seemingly very little to do with starting the 

 process of germination. We are familiar with the fact that the 

 seeds of many plants that fail to germinate in the summer of their 

 production habitually germinate under apparently less favourable 

 conditions of temperature in the following spring. This is attributed 

 by botanists to the immaturity of the seed on first falling from the 

 plant, a further period of maturation being necessary before, under 

 any conditions, germination is possible. 



We see this also well illustrated in the floating seeds and fruits 

 of the Thames drift. Most of them fail to germinate in the drift at 

 the end of the summer and the beginning of autumn, and defer the 

 process until the following spring, when they germinate freely in 

 the water under much cooler conditions than those which they 

 experienced in the early part of their flotation in the drift. There 

 are, however, exceptions to this rule. Plants like Caltha palustris,. 

 for instance, are rarely represented in the spring seed-drift of ponds 

 and rivers, because most of the fruits or seeds germinated soon after 

 falling into the water in the previous summer. 



In most of my sea-water experiments in England the immersion 

 had a very marked influence, not in causing premature germination 

 and destroying the germinating capacity, as often happens with the 

 floating seeds of Convolvulaceae and Leguminosae, especially in the 

 tropics, but in postponing without injury to the seed the process of 

 reproducing the plant. Such seeds or fruits when placed in fresh 

 water after many months of flotation in sea-water germinated very 

 freely in a few days, whilst those left in the sea-water under precisely 

 the same conditions remained unchanged, This is true of many of 



