RHIZOPHORA MANGLE 



99 



New World was very small, namely, 3 per 1000 {Plant Dispersal, 

 p. 450). 



The Length attained on the Tree by Seedlings of Rhizo- 

 phora mangle. — In Jamaica, as in Fiji and Ecuador, I found that 

 the average length attained by seedlings on the tree, the measure- 

 ments being taken from the base of the plumule, was from nine to 

 ten inches. In all three regions, when growing in sheltered situations, 

 they may attain a length half as long again. But it would seem that 

 this maximum is at times greatly exceeded in the New World. Thus 

 I found washed ashore on the weather side of Tobago, mingled with 

 much Orinoco drift, several seedlings sixteen to eighteen inches long, 

 and in one case twenty-two and a half inches in length. It is quite 

 possible, however, if these seedlings had been a long time afloat in 

 the sea, that their hypocotyls may have grown in length, a subject 

 discussed above. 



The Absence of Dimorphism in Rhizophora mangle in 

 Jamaica and other West Indian Localities. — In different 

 localities in the West Indies, as in Jamaica, the Turks Islands, and 

 Grenada, I endeavoured to ascertain if Rhizophora mangle exhibited 

 the dimorphism displayed by the species in Ecuador. In my book 

 on Plant Dispersal (pp. 445, 487) it is shown that in Ecuador 

 there are two forms : the one " mangle chico," ten to fifteen feet 

 high, growing in the seaward and landward margins of the swamps ; 

 the other " mangle grande," which attains a height of sixty or 

 eighty feet and composes the interior of the swamp. The last in 

 some of its characters approaches Rhizophora mucronata, the Asiatic 

 species. However, after careful inquiry in the Black River and 

 Savanna-la-mar districts of Jamaica, I could not discover any per- 

 sistent evidence of dimorphism. Although there was often a con- 

 siderable contrast in height and size between the Rhizophora trees 

 fronting the sea and those growing in the midst of the swamp and on 

 the banks of estuaries, the former frequently only ten or twelve feet 

 high and the latter attaining heights of sixty or seventy feet, the 

 floral characters as a rule remained much the same. Only in a few 

 cases did there seem a tendency to the development of the " mangle 

 grande " type in the taller trees. It may be that Rhizophora 

 racemosa (a form of Rh. mangle where the stalk of the inflorescence 

 branches two or three times), which was long ago differentiated by 

 botanists, may answer to the " mangle grande " type. The two are 

 separated in Hooker's Niger Flora. However, the " mangle chico " 

 is evidently the West Indian form. The plants of the Turks Islands 

 were all of this type, and, as far as examined, those of Grenada and 

 Tobago. On the parts of the coast of Porto Rico visited by Dr. 

 Millspaugh the tree " seldom attains a growth of over ten feet in 

 height " {Plantar Utowano3, Pt. I.). In the West Indies I never 

 came upon any seedless form of Rhizophora, such as I have described 

 in the case of the 44 Selala " of Fiji {Plant Dispersal, p. 443). 



On the Influence of Varying Degrees of Salinity on the 

 Station of Rhizophora mangle. — A promising field of inquiry 

 would lie in the systematic determination with the hydrometer of 

 the influence of varying degrees of salinity on the distribution of 



