MISCELLANEOUS PLANTS 



183 



BORRICHIA ARBORESCENS, DC. 



This is a maritime Composite shrub, usually two to three feet high y 

 which is very typical of the warm regions of the New World. It 

 belongs to a genus exclusively American and comprising only two 

 allied species, of which the present one ranges over the West Indies 

 and tropical continental America, whilst the second (B. frutescens r 

 DC.) grows in the Southern United States and in Mexico, both species, 

 being indigenous seaside plants in Bermuda (Chall. Bot., II., 45)*. 

 Although we are only concerned here with the wide-ranging species^, 

 it is highly probable that the results of my observations on the 

 dispersal capacities will apply to both. 



This shrub commonly frequents rocky stations at the coast, but 

 it also grows on sandy beaches and on the dunes in their rear. It 

 often presents in the same locality two forms, one with glabrous, 

 foliage and the other with leaves covered by a silvery down; but 

 both kinds of leaves may occur on the same individual. The writer 

 specially studied the plant from the dispersal standpoint in Jamaica 

 and in the Turks Islands. Its most critical habitat is in the Florida 

 sand-keys, where we see in operation the earliest stage of plant- 

 stocking in these regions, so well observed by Mr. Lansing and 

 described by Dr. Millspaugh (Field Columbian Museum, publ. 118, 

 Bot. Ser., 1907). After the mangroves it takes a place amongst the 

 first seven or eight strand plants that occupy the newly formed 

 islets in these seas. 



The next critical habitat is Bermuda, since the question of the 

 fitness of the fruits for transport by currents across broad tracts; 

 of sea is at once raised. The achenes, including the short crown,, 

 are from 4 to 5 mm. long ; but there are no hairs nor any means off 

 attaching the fruits to plumage. Looking to the currents for a* 

 possible explanation of the wide range of the plant, I tested the 

 buoyancy of the fruits both in Jamaica and in the Turks Islands. 

 In my Jamaica experiments they sank after soaking in sea-water 

 for a day or two. In those made in the Turks Islands on the plants- 

 of that group, the fruits floated on the average six or seven days r 

 the limit being ten days; but in a later experiment in England on- 

 fruits of the same set, which had been kept for fifteen months, they- 

 floated on the average nine or ten days, the limit being seventeen 

 days. In such experiments it is requisite to select the achenes. 

 very carefully, since from insects and other causes it is often not 

 easy to find achenes with sound seeds. 



In the light of these results it is evident that the original fruits 

 could not have reached Bermuda by their own floating powers, 

 a passage, as shown in Note 14 of the Appendix, that would usually 

 occupy nearly three months. Nor can we appeal to the agency of 

 sea-birds, since the dry fruits would not be likely to be swallowed by 

 them, whilst, as already remarked, they do not adhere to plumage*. 

 We are thus driven to conjectures. It may be suggested that the 

 achenes were accidentally introduced into the Bermudas with the 

 salt brought from the Turks Islands in the seventeenth century.. 

 In those times there was a regular trade between the two groups in 



