86 A NATURALIST IN THE PACIFIC CHAP. 



the seeds and fruits found in the Thames drift, such as those of 

 Ranunculus repens, Lycopus europaeus, Rumex, &c. A striking 

 instance was also afforded by the seeds of Arenaria (Honckeneya) 

 peploides, where seeds transferred directly to fresh water, after many 

 months flotation in sea-water, germinated in a few days ; whilst 

 those left in the sea-water remained unchanged. This subject is 

 discussed at length in Note 19, and needs no further mention here. 

 If the seeds of many plants in Great Britain postpone through 

 immaturity their germination to the following or even to the second 

 spring, it goes without saying that this does not exclude tempera- 

 ture as the ultimate determining factor in germination. The im- 

 maturity of seeds adds another link to the series of the germination- 

 range in plants. This range begins with the plants where germina- 

 tion takes place on the tree and the seedlings hang suspended from 

 the branches, as in the typical mangroves Rhizophora and Bruguiera. 

 Here, as is shown in Chapter XXX., there is evidently no period of 

 repose between the completion of the maturation of the seed and 

 the commencement of germination. The range ends with the 

 detachment of immature seeds which ripen apart from the parent 

 plant, and may postpone the germinating process for months and 

 -often for years. All intermediate stages exist between these two 

 ^extremes. Thus the seedling may at once detach itself from the 

 parent as in Avicennia, or the germinating process on the plant 

 -may be limited to the protrusion of the radicle as in Laguncularia, 

 or the seeds may be quite mature and ready to germinate as soon 

 as they fall to the ground, as we find with many small seeded 

 ^plants. All the stages, of which only a few are here indicated, are 

 full of suggestiveness for the student of plant-life. 



This subject is dealt with from other standpoints in Chapter 

 XXX., but the reader will now see more clearly what was meant 

 when I said that the study of the behaviour of the floating seed leads 

 us to the borderland of vivipary. In this range of the germinating 

 process we may possess an epitome of the history of the climatic 

 conditions of plant-life from an early era in the world's story, 

 beginning with those ages when perhaps under the uniform 

 conditions that then prevailed, all plants were more or less coast- 

 plants and more or less viviparous, and coming down to the present 

 era when with an extensive and varied land-surface there is great 

 variety both in climate and in the range of germination. The 

 mangrove-swamp and its viviparous trees would thus represent 

 from this point of view a condition of things once more or less 

 universal on the globe. 



