1 90 A NATURALIST IN THE PACIFIC CHAP. 



Keeling Atoll where the plant has found a home. It is to be 

 noted that the plant collected by Darwin in this atoll was identified 

 by Prof. Henslow as C. bonduc ; but the plant observed by me 

 was more like C. bonducella, and the stranded seeds collected by 

 me were referred at Kew to this species. Some curious considera- 

 tions arise from the fact that although, just as in the Keeling 

 Islands, the plants of C. bonducella have evidently established 

 themselves from drift seed in one locality in the Bermudas, they 

 do not seem to have done so either on the shores of Krakatoa, or 

 of St. Helena, where, although they are frequently washed ashore, 

 Mr. Melliss never met with an instance of germination (see Bot. 

 Chall. Exped. iv, 300, and Penzig). This is doubtless in part the 

 result of the destructive efforts of the crabs, which, as I have shown 

 in my paper on Keeling Atoll, nibble off the shoots of many ger- 

 minating seeds in beach drift. 



The readiness or non-readiness of seeds to germinate on a 

 beach, and the nature of the conditions essential for the process, are 

 matters that are directly concerned with their effective dispersal 

 by currents. On account of the stony character of the seeds of 

 these two species, it might be expected that germination would 

 only take place under exceptional conditions. It should, however, 

 be observed that the fine transverse striae on their outer surfa-ce 

 represent original fissures or cracks in the epidermis of the soft 

 immature seed ; and as such may be regarded as lines of weakness 

 in the seed-tests. If a pod is opened before the seeds are mature, 

 we find the seeds about twice the size of maturity, and so soft that 

 they can be indented by the nail. The transverse striae that mark 

 the mature seed are displayed as indistinct cracks in the epidermis ; 

 and if the immature seed is exposed to the sun, in a few hours 

 these cracks gape widely, and the seed has the grooved appearance 

 of a top. If a pod opens prematurely on a plant, as sometimes 

 happens, the immature seeds will be noticed with the epidermis 

 scaling off. It is evident that the "setting" or the induration of 

 the seed-coats and the final great contraction of the seed take 

 place in the pod before dehiscence. From these remarks it would 

 seem probable that seeds lying exposed to the fierce rays of the 

 sun on a tropical beach would be liable to develop cracks along 

 the old fissures, and that such cracks by permitting the entrance of 

 moisture would favour germination. 



My experiments show that high temperature under moist con- 

 ditions will not of itself induce germination or in any way affect 

 the seed. Thus in two sets of experiments, in 1890 and 1902, I 



