ON THE MODES OF DISTRIBUTION OF PLANTS. 365 

 ON THE MODES OF DISTRIBUTION OF PLANTS. 



Bt JOSEPH F. JAMES. 



THE study of the geographical distribution of plants over the earth 

 is one of the most profound interest, not only to the botanist but 

 to mankind in general. To the former it is of especial interest on 

 account of the intimate relations existing between it and the origin of 

 the different species of plants. Where we find an isolated example of 

 a group of plants existing in one country, while its nearest congeners 

 are in another perhaps thousands of miles off, we naturally feel inter- 

 ested in trying to discover the cause of this wide separation, and the 

 means by which the plant has reached its present location. It is to 

 the means of distribution that we shall devote this paper. 



It is a trite remark that although there may be places identical in 

 temperature, in soil, in humidity, and other circumstances governing 

 the stations of plants in both North America and Europe, and in South 

 America and Africa, still it does not necessarily follow that the species 

 of plants in these identical localities are alike or even at all similar. 

 Indeed, researches show it to be rarely or never the case. In almost 

 every country, however, there seems to be a certain though sometimes 

 a small proportion of plants which are found in other and distant 

 parts of the world. For instance, Mr. Brown found that, out of 4,100 

 species of plants then known to inhabit Australia, 1G6 were identi- 

 cal with those of Europe, and that the greater proportion of these 

 were cryptogamous plants, while those that were not were plants 

 common to the intervening regions.* There are 359 indigenous 

 plants out of the 2,277 phaenoganis given in the last edition of Gray's 

 " Manual," which are also indigenous to Europe. A number, too, of 

 the plants of eastern North America are common to northeastern Asia, 

 China, Japan, and India. Out of a collection of 600 plants from the 

 river Congo in Africa, Dr. R. Brown found thirteen which also grew 

 on the opposite coasts of Brazil and British Guiana. f No less than 

 one fifth of the algse from the Antarctic seas, exclusive of the New 

 Zealand and Tasmanian groups, have been identified by Dr. Hooker 

 with British species.^ A few of the most remarkable cases of distri- 

 bution of identical species will no doubt be of interest here. Saave- 

 gesia erecta grows in the Antilles, in Brazil, in Madagascar, and in 

 Java ; Scirpus maritimus grows in North America, in Europe, in 

 western India, in Senegal, at the Cape, and in Australia ; Brasenia 

 peltata grows in the United States, in Japan, in eastern India, and in 



* Lyell, "Principles of Geology," ii., p. 387. 



f Lyell, ibid., ii., p. 394. 



% Lyell, ibid., ii., p. 3S9. 



Jussieu, " Elements of Botany," p. 718. 



