April, 1916. Alacran Reef — Millspaugh 427 



In order to check up the record of the Admiralty survey I cut down 

 the two apparently oldest shrubs and made cross sections of the trunks.* 

 In so far as the annual rings may determine they proved to be 25 and 

 30 years old respectively. Should the rings prove a faulty record the 

 error would be in favor of a shorter period of growth, it is therefore 

 certain that the shrubs did not exist there at the time of the survey, the 

 notes of which state: "Grass and samphire only." One shrub, judged 

 to be not over four years old, grew on the southern shore of Chica. 



At the period of ripened fruits the fruiting twigs of this species be- 

 come quite brittle and, as the plant frequents the immediate sea shore, 

 these twigs are often broken off by heavy winds and blown into the sea. 

 That they float away and are later washed ashore on the crests of waves 

 was apparent in the "wash line" on the weather side of Perez where I 

 found a large quantity of fruiting twigs newly come ashore. This 

 leaves no doubt of the species being bodily aquavectent. 



4. Cakile alacranensis Millsp. Field Mus. Bot. 2:130. 



This new species of the shoal differs from all others known in its 

 short silique bearing four channelled lines instead of 8 or more (angles 

 in most species); in its upper joint being globose-apiculate and very 

 turgid; in its infundibuliform lower joint which is but httle more than a 

 swelling of the pedicel, and in having its seeds dotted with brownish 

 punctae. The leaves are yellowish-green, spatulate-lanceolate tapering 

 to a partly clasping petiolar base, and entire or rarely slightly crenate or 

 crenate-dentate at the apex. 



This species grows upon the north strand of Allison Island; on the 

 north weather strand of Chica and Pajaros; and on the southern half of 

 the weather strand of Perez.f While the plants from both Perez and 

 Pajaros are large fruit producers they have a sickly yellow appearance 

 compared with the fresh, cool green of those of Chica. It is evident that 

 the original habitat of this species is either Allison Island, or possibly 

 unexplored Utowana Cay, as the distribution of the plants on the south- 

 ern cays is quite apparently more recent. 



It appears to me that this species is evolving for the piu-pose of 

 more highly developed aquavectence. The upper, or floating joint, is 

 certainly developing far more rapidly than the lower, or fixed, joint of 

 the fruit : the upper at the expense of the lower. 



Distributionally the upper joint of the fruit is aquavectent while the 

 lower, being fixed upon the rhachis and on that account not adapted to 



*These sections are mounted on the herbarium sheets of the species from this 

 island in the Museum herbariiun. 



tThe treatment of Cakile in Field Mus. Bot. 2:43 and 2:128-130 to the contrary 

 not withsta nding . 



