64 USEFUL PLANTS OF GUAM. 
tivated, but very little has been done to fix the species and varieties 
and to compare those growing in different parts of the world. \ Yams 
are dicecious, and the flowers of many recognized varieties are imper- 
fectly known. In some cases the flowers of but a single sex have been 
described; in others the fruit has never been observed, and in others 
only the tubers are known. Sir Joseph Hooker,“ who has done much 
to straighten out the Indian species, writes as follows: 
The species of Dioscorea are in a state of indescribable confusion, and I can not 
hope to have escaped errors in the determination and delimitation of the Indian 
ones, to which T have devoted much labor. The Roxburghian food-yielding species 
are for the most part indeterminable, and, except. through a knowledge of them as 
cultivated in India, they can not be understood. No doubt some of the species 
described by me have other earlier names in the Malayan flora than | have given; 
but the Malayan species are even more loosely described than the Indian. The 
Wallichian collection is very complete, but the species are often mixed. 
What has been said of the Indian yams applies also to those of the 
Pacific islands, and is also true of the many varieties of Musa and 
Artocarpus. Nearly every collector gives a list of named varieties of 
Dioscorea, Musa, and Artocarpus in the vernacular of the various 
localities visited, but scarcely any attempt has been made to fix these 
varieties and to bring together the various kinds from different local- 
ities for comparison. These must be studied in the countries where 
they are found and should be represented in collections not only by 
series of botanical specimens of the flowers, fruit, leaves, and roots 
(in alcohol, when necessary), but by photographs of the fresh plants, 
including representations of the flowers, fruits, tubers, etc., of natural 
size or according to some definite scale of reduction or enlar eement. In 
this way only will it be possible to bring together and compare species 
and varieties from India, Australia, the Malayan and Pacific islands, 
Africa, and America. 
SCREW PINES. 
The Pandanaceae are known no better than the yams. Some of them 
are propagated asexually for the sake of their textile leaves, and much 
confusion exists among the species. Very few have been described. 
Warburg has done much to delimit the species and varieties and clear 
up questions of synonymy, but there remains much more to be done. 
In his monograph of the Pandanaceae’ Warburg mentions only one 
species, Pandanus dubius Spreng. (Llombronia edulis Gaudich.), 
occurring in the Marianne Islands, and does not refer to the textile 
species with glaucous leaves (the aggak of the natives), which has been 
cultivated in Guam from prehistoric times (Pl. VII), nor the fragrant- 
fruited species with bright green leaves (/afé), which is one of the 
most common pk ints of the island (Pl. LX). As only one sex of the 
«Hooker, Flora British India, vol. 6, pp. 288- 289, 1892. 
>’ Warburg, Pandanaceae, in Engler, Pflanzenreich, vol. 4, p. 9, 1900, 
