XYLOMELUM 
611 
Wyethia Nutt. Compositae (v). 12 sp. western N. Am. 
Xanthium (Tourn.) Linn. Compositae (v). 4sp. temp, and trop. They 
have been so widely distributed by man (unintentionally) that it is hard 
to discover their native place. The firs, are in unisexual heads, which 
are single or in axillary cymes, the $ at the ends of the branches. The 
$ head has 2 firs. , enclosed in a prickly gamophyllous involucre, only 
the styles projecting from it through openings in the two horns of 
the involucre. The fruits are enclosed in the hard woody involucre, 
which is covered with hooks and is admirably suited to animal-distri- 
bution. One sp. has gradually spread in this way from the East of 
Europe. “In 1828 it was brought into Wallachia by the Cossack 
horses, whose manes and tails were covered with the burrs. It tra- 
velled in Hungarian wool, and in cattle from the same region, to 
Regensburg, and on to Hamburg, appearing here and there on the 
way.” Strenuous laws for its extirpation have been enforced in South 
Africa, where at one time it had become so common as seriously to 
impair the value of the wool. 
Xanthochymus Roxb. = Garcinia Linn. 
Xanthophyllum Roxb. Polygalaceae. 40 sp. Indo-mal. Ovary i-loc. 
with parietal placentae. Nut one-seeded. 
Xanthorrhiza Marshall = Zanthorhiza L’Herit. 
Xanthorrhoea Sm. Liliaceae (in). 11 sp. Austr. The best known is 
X. hastilis R. Br., the grass-tree or black -boy, a characteristic plant 
of the Austr. vegetation (p. 196). It has the habit of an Aloe or 
Dasylirion, with a long bulrush-like spike of firs, (really cymose as 
may be seen from the many bracts on the individual flr.-stalks). 
Perianth sepaloid (X. is placed in Juncaceae by Benth. -Hooker). 
From the bases of the old leaves trickles a resin, used in making 
varnish, sealing-wax, &c. 
Xanthosia Rudge. Umbelliferae (1). 17 sp. Austr. The umbels in 
some sp. are reduced to single firs. 
Xanthosoma Schott. Araceae (vi). 20 sp. trop. Am. Large herbs 
(fig. in Kerner’s Nat. Hist.). X. appendiculatum Schott has a second 
blade at the back of the leaf, united with the chief one along the mid- 
rib, and much smaller than it. A pocket is thus formed whose use is 
unknown. The phenomenon is due to a tangential division of the 
embryonic leaf. Firs, monoecious, naked ; sta. in synandria. 
Xanthoxylum J. F. Gmel. = Zanthoxylum Linn. 
Xeranthemum Tourn. ex Linn. Compositae (xi). 6 sp. Medit., Orient. 
Xiphion Tourn. ex Mill. = Iris Tourn. 
Xylomelum Sm. Proteaceae (11). 4 sp. Austr. The fruits are known as 
wooden pears, being of the size of a large pear, and looking at first 
glance as if they were edible. Inside is found a thick wall of woody 
tissue enveloping the winged seeds. It splits open along the posterior 
side. This sort of fruit is found in several Proteaceae and is looked on 
as an arrangement for protection of the seeds from the drought (p. 168). 
39—2 
