Vol. I] 



STEWART— BOTANY OF THE GALAPAGOS ISLANDS 



235 



these animals are large and unable to swim, they are able to 

 keep afloat for a considerable time, long enough to float them 

 from the mainland to the islands if we assume that the ocean 

 currents were as strong and had the same general trend in past 

 geological times as they have now. The ability that these 

 animals have of living without food for a considerable time 

 greatly strengthens this view. During our homeward voyage 

 from the islands, in the autumn of 1906, our live specimens of 

 tortoises went for over a month without food, a time suffi- 

 ciently long, under favorable conditions, to float an individual 

 from the mainland of North America to the islands, if one 

 should happen to get adrift. It would not be absolutely neces- 

 sary that both male and female tortoises should be introduced 

 on the islands to start the race, for this could be accomplished 

 if a single female specimen containing fertilized eggs should 

 be cast upon the shores of the islands. 



Turning to the botanical side of the question, we would natu- 

 rally expect that of the eighty families of vascular plants found 

 on the islands some few at least would have approximately the 

 same number of genera and species as are found in these same 

 families on the mainland. The following table shows all of 

 the families of vascular plants which contain ten or more 

 species, varieties, forms, and indeterminate species. 



Families of Galapagos Plants with Ten or More Species, 

 Varieties, or Forms 



Rank 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 



Family 



Filices 



Compositae .... 

 Euphorbiaceae . 



Gramineae 



Leguminosae . . . 

 Amarantaceae. . 

 Cyperaceae. . . . 



Solanaceae 



Rubiaceae 



Malvaceae 



Boraginaceae . . . 

 Convolvulaceae 

 Verbenaceae . . . 



No. of Species, 



Varieties, and 



Forms 



77 

 65 

 50 

 49 

 45 

 33 

 25 

 19 

 22 

 19 

 20 

 15 

 13 



Indeterminate 



4 



10 



6 



Total 



77 

 69 

 60 

 55 

 53 

 33 

 28 

 26 

 23 

 22 

 21 

 15 

 15 



