174 PLANTS, SEEDS, AND CURRENTS 



from some vessel near the Norwegian coast ; whilst it is scarcely- 

 likely that the heavy nut when fresh could have much buoyancy. 

 This is indicated in one of my experiments. I placed in sea- water 

 some sound nuts which had been gathered rather over a year. After 

 a few days the pericarp began to soften, and in ten days all the nuts 

 were at the bottom of the vessel, a week being the average flotation 

 period. Empty nuts are much lighter and might float longer. 



Anona palustbjs, L. 



The genus Anona, or, as it is now usually written, Annona, has 

 been fortunate in its latest monographer, Dr. W. E. Safford, who 

 has recently published in volume 18 of the Contributions from the 

 United States National Herbarium for 1914 a classification of the 

 genus. Here we are mainly concerned with the littoral and estuarine 

 tree above named ; but from the distribution standpoint it cannot be 

 treated without some reference to a few of the general features of 

 the genus to which it belongs. 



" The genus Annona " (writes Dr. Safford, p. 4) " is confined 

 almost exclusively to tropical and subtropical America. At an early 

 date, however, certain species were introduced into the warmer 

 regions of the Old World for the sake of their edible fruits, and 

 were described as distinct. In addition to these there are a few 

 species endemic in tropical Africa." The author gives no numerical 

 account of the distribution of the genus in his paper. Failing this, 

 a general statement of the results for about 120 species named in 

 the Index Kewensis may be given. Here about 100 species are 

 exclusively American. Of the balance most are tropical African, 

 and the rest occur in Madagascar, the Mascarene Islands, Ceylon, 

 China, and Malaya, with one species, A. palustris, both American and 

 African, the only species common to the Old and the New Worlds. 

 Some emendation is, however, here required respecting the few 

 Asiatic species named in the Index Kewensis, since Dr. Safford 

 informs me that " there is no endemic Anona in Asia. . . ." The 

 manner in which the edible species, the Sops, the Custard Apples, 

 the Cherimoya, etc., have been spread over the world by man, not 

 only in recent times but by the early European navigators, suggest 

 that human agency may have been effective in this direction, even 

 in prehistoric times. (Dr. Safford tells me, in a letter since received, 

 that " certain economic species were introduced into India at a 

 very early date.") 



It is a significant fact that the only species which links together 

 the Old and the New Worlds, the cultivated species being excluded, 

 is one of the plants of the mangrove association, namely, Anona 

 palustris, a tree that finds its home in estuaries and in coastal swamps. 

 As far as I can ascertain there is no other species that could be 

 regarded as a littoral plant. There are one or two species like 

 A. paludosa, Aubl., that grow in marshy situations at the coast, 

 but they also occur inland. Nor are there any plants that are 

 exclusively confined to the vegetation bordering the sandy beaches. 

 Where such plants grow in sandy plains at the coast they belong 



