248 PLANTS, SEEDS, AND CURRENTS 



occurs on both coasts of Africa. We are thus face to face with 

 problems of a different nature. 



This is seemingly not such a well-defined genus as Sccevola. It 

 holds more than 120 species, distributed over the tropics and sub- 

 tropics of the globe; and since the New World possesses its own 

 peculiar species, it may be inferred that Tournefortia gnaphalodes 

 could have had an independent origin on this continent. Hemsley 

 states that there are several littoral species. One of these, as 

 I infer, is T. sarmentosa, Lam., which extends from the Philippines to 

 North Australia and occurs also in Mauritius and in the Seychelles 

 (Bot. Chall, IV., 168). 



Like the two shore species of Sccevola, those of Tournefortia possess 

 fruits endowed with great floating powers, and are thus well fitted 

 for dispersal by currents. However, they differ from the Sccevola 

 plants in that the fruits of both species exhibit the same type of 

 buoyancy. There is a much greater resemblance, both in habit 

 and general appearance, between the two shore species of Tournefortia 

 than in the case of the other two plants. Covered with hairs, which 

 give them a silver-grey hue, these shrubs form a conspicuous feature 

 in the shore landscape, their height ranging usually up to five or 

 six feet, but much reduced in exposed situations. 



I will now deal more in detail with these two species of Tournefortia 

 from the standpoint of dispersal by currents. Both of them possess 

 dry drupaceous fruits, measuring about seven millimetres in the 

 case of T. gnaphalodes and somewhat less in the case of T. argentea. 

 When naturally dried, these fruits separate with a little pressure into 

 two hemispherical pyrenes, and it is in this condition, but bared of 

 their outer dark skin, that they usually occur in the old drift of beaches. 

 Each pyrene displays a suber-like exocarp, in which lies imbedded a 

 small two-celled stone, each cell usually containing a seed. Deprived 

 of its outer covering the stone sinks. 



[Particulars relating to T. argentea will be found in Schimper's 

 work on the Indo-Malayan strand flora (p. 174), in my Plant Dispersal 

 (p. 108, etc.), and in my paper on Keeling Atoll in the Journal of the 

 Victoria Institute (1889)]. 



A familiarity with both species in their homes enables me to treat 

 them together here. The fruits of both plants, entire and in halves, 

 are of common occurrence in the smaller drift of beaches on which 

 they grow. They cover the sand in quantities beneath the bushes, 

 and the strong winds scatter them over the beach. So frequent were 

 they on some of the beaches of the Turks Islands that they were 

 to be noticed in every handful of sand. Under the shrubs they are 

 apt to germinate, as was often indicated on Grand Turk by the 

 shrivelled projecting radicles that had withered up before they could 

 establish themselves in the sand. I noticed both on Keeling Atoll 

 and on Grand Turk that the pyrenes are at times mixed with the sand 

 washed into the crevices of stranded logs. This matter is especially 

 discussed in my paper on Keeling Atoll ; and it is there shown that 

 floating pumice must also often assist dispersal in the same manner. 

 But although drifting logs and floating pumice often aid dispersal, 

 they do not determine it, since the buoyant fruits of these two 



