GREAT WHITE POPLAR-TREE. 253 
In some of the rich lands of South America, yams 
are said to grow to the weight of iifty or sixty 
pounds each ; and are so productive that an acre 
of ground planted with them has been known to pro- 
duce roots to the weight of from 20,000 to 30,000 
pounds. Yams are propagated by setting the eyes, in 
the same manner as we plant potatoes ; and, in six or 
eight months, they arrive at maturity. 
When they are dug out of the ground, they are, for 
a little while, exposed to the sun to dry ; and if, after 
this, they be packed in casks full of dry sand, they 
may be preserved, without injury, for many months. 
They are consequently often used as sea-store for ves- 
sels about to sail on long voyages, and are frequently 
brought into England. Several attempts have been 
made to cultivate yams in this island ; and these have 
been attended with a certain degree of success in the 
counties of Mid-Lothian, Perth, and Stirling in Scot- 
land, where they are used for the feeding of cattle. 
There are two kinds, one red, and the other white. 
The former of these contain a more nutritive food than 
the latter, though their flavour is much less excellent. 
With the negroes, in the West Indian islands, the yam 
is a very important article of food. When roasted, it 
is so wholesome and nutritive that it is preferred by 
them even to bread. Like potatoes, yarns may be 
converted into bread, by mixture with a portion of 
wheat or barley flour. They are sometimes made into 
soup, puddings, and other useful dishes. 
OCTANDRIA. 
262. The ABELE, or GREAT WHITE POP LAR- 
r REE (Populus alba, Fig. 74), is a British tree which 
grows in hedges and woods, near brooks, and is known by its 
leaves being nearly triangular, irregularly jagged at the edges, 
and cottony underneath. 
The quickness of growth of this tree is so great that 
it will sometimes make shoots from eighteen to twenty 
