AGAVE IN THE WEST INDIES—TRELEASE. 11 
the Viviparae to the south. To the newer Bahamian table a transient connection with the 
Cuban land mass seems to have given the parent form of the group of species peculiar to the 
islands into which this intricately canyoned plateau has now settled. The segregation of the 
Viviparae from the dominant Caribbean form appears to have been effected early under conti- 
nental influences, if they be not of Central American origin; that of the Antillares from the 
dominant Antillean form may be ascribed to the diversified physiography and attendant 
climatic differences of the great island, Cuba. 
Successive disruption of each of the principal land masses, as subsidence continued (pls. D 
and E), has clearly afforded progressive isolation, with opportunity for local’ evolution, until 
each natural division of the archipelago now possesses its exclusive fleshy-leaved type, with 
subtypes on the great islands and next the South American continent; and each island or 
group of islands on a common bank possesses its distinctive species or group of species in which 
foliage, flowers, and fruit show diverse and intricate combinations of the group characters. 
The genus, therefore, here epitomizes unusually well the facts of insular evolution, a process 
which is fairly capable of division into three periods represented by: (1) The major groups, 
(2) such minor groups as extend through islands on a common bank, like the chain from Anguilla 
to Dominica, and (3) the species of which these groups consist to-day (see the table facing p. 1). 
Their source is so unquestionably North American and their limitation by water barriers is so 
marked as to leave little room for doubt as to the former existence of the much disputed 
Antillean union between the continents, whether or not in the exact form here outlined.! 
SPECIFIC CHARACTERS. 
Because so commonly described from garden specimens, frequently young, the species of 
Agave that are currently listed are often hard to recognize in nature and it is very important 
to understand those differences which may be called characteristic. The constancy of agree- 
ments and differences is so marked in such well-known and commonly grown species as A. 
americana, A. picta, A. Victoriae Reginae, A. filifera, A. fourcroydes, etc., as to warrant confi- 
dence in the general stability of species on the one hand, while on the other the changes that 
plants undergo from youth to age and the differences that appear between seedlings of a common 
parentage as well as between plants ascribed to a single species indicate the necessity of caution 
in either stating or accepting characters as of absolute value, and suggest mutational plasticity. 
TRUNK.? 
In general, the trunk or caudex possesses little taxonomic significance in Agave, for, though 
many species are conveniently spoken of as acaulescent, the leaf bases as a rule cover a trunk 
which, denuded, is seen to be of measurable length. Such differences as the so-called acaules- 
cent and subacaulescent species show (cf. A. viipara, pl. 1, and A. evadens, pl. 9) are chiefly 
due to the number and relative thickness of the leaves and the degree of their persistence until 
the maturity of the plant. Marked exceptions only are of appreciable diagnostic value; such, 
for example, as those offered by A. fourcroydes (pl. 110), A. attenuata, and especially the truly 
arborescent A. Karwinsku,*? which have a distinct and much elongated trunk finally denuded 
or covered with dried leaves below. 

1 Apart from the many analyses of the boreal and austral elements in the general flora and fauna of the West Indies, reference may be made 
here to the newly published Phytogeographic Survey of North America by Harshberger (Engler and Drude, Vegetation der Erde, vol. 13, 1879), 
with its bibliography, as containing important data on this subject. The marked division in the flora corresponding to the Anegada Passage is 
noted by Eggers in his account of the Flora of St. Croix and the Virgin Islands (Bull. U. S. Nat. Mus., No. 13, 1879, pp. 13-16, etc.), and Hitch- 
cock (Rept. Missouri Bot. Gard., vol. 4, 1893, p. 158, etc.) devotes several pages to figures that are very suggestive. The closer biological 
connection of Jamaica with Haiti than with Cuba is indicated by Barbour (Bull. Mus. Comp. Zool., vol. 52, 1910, p. 277), and a parallel to the 
entrance of Agave from Yucatan into Cuba rather than from Central America into Jamaica is indicated on a map illustrating the migrations of 
South American fresh-water fishes which accompanies Eigenmann’s Catalogue of the Fresh-water Fishes of Tropical and South-Temperate America 
(Scott, Rept. Princeton Univ. Exped. to Patagonia, vol. 3, 1910). 
2Engelmann, Trans. Acad. Sci. St. Louis, vol. 3, 1875, p. 293; Bot. Works, 1887, p. 301. 
3 Rept. Missouri Bot. Gard., vol. 18, 1907, pl. 30. 
