172 PLANTS, SEEDS, AND CURRENTS 



Jarnesiana has here been taken as a sample of a small group of 

 cosmopolitan tropical and subtropical plants, including such as 

 Hibiscus tiliaceus and Thespesia populnea, which, though often 

 differing greatly in other particulars, are linked together by the 

 difficulties which their distribution presents. Equally at home at 

 the coast and inland, and all capable, though to a varying degree, 

 of dispersal by currents, there is always more than a suspicion that 

 man has assisted for ages either directly or indirectly in their dis- 

 tribution. Over all of them hangs a doubt as to their birthplace, 

 since they behave as indigenous plants over most of the warm regions 

 of the globe. In their present range they seem to be quite inde- 

 pendent of the development centre of the genus. If the botanist 

 places the plant concerned in one hemisphere, the errant species 

 presents itself as to all appearance an indigenous plant in the other. 

 The student of distribution quarrels with all of them in one region 

 or another, since they figure too frequently as disturbing factors in 

 his speculations on the history of a flora. 



Both Hibiscus tiliaceus and Thespesia populnea are treated in a 

 later page, but with less detail as the writer hopes to take up the 

 further study of the story of their travels around the globe. Their 

 history is bound up with that of aboriginal peoples, and they raise 

 somewhat different issues than does the species of Acacia with which 

 we have been concerned. The names of Hibiscus tiliaceus and 

 Thespesia populnea are part and parcel of the native languages 

 around the tropics, and we can almost detect a linguistic affinity 

 between those of the New and the Old World. On the other hand, 

 Acacia farnesiana is a nameless plant, as the philologist would 

 express it, around the tropics of the globe. It has names, it is true, 

 but not names that belong to the language of the aborigines in whose 

 country it may now grow. It has been a great traveller, but its 

 story is bound up rather with the continents than with islands, 

 rather with early civilisations than with states of barbarism. From 

 the circumstance that it has been identified with the " Small Acacia " 

 of Dioscorides, and has been even supposed by some to have been 

 represented by its flowers in Egyptian tombs (Von Mueller, Ecctr. 

 Trop. Plants ; De Candolle, Geogr. Bot.) 3 we may have to face quite 

 other issues. 



Ambrosia crithmifolia, DC. (A. hispida, P.) 



This composite beach plant ranges all over the West Indies, 

 including the Bahamas and the Florida keys and the continental 

 shores of the Caribbean Sea. Growing prostrate on the sand with 

 its flowering spikes rising six to twelve inches in the air, it gives a 

 peculiar aspect to the surface, reminding one a little, as regards the 

 foliage effects, of an English sand-dune covered with Matricarias. 

 When it carpets extensive tracts of sandy plains bordering the sea, 

 the aromatic fragrance of the plant is often borne far to seaward 

 by the wind blowing off the shore. 



Detached from the parent plants the small dry fruits, enclosed in 

 the persistent involucre, occur in numbers in the sand of beaches, 



