60 NATURAL HISTORY OF THE FARM 
inedible, and a few like the water 
hemlock (Fig. 33) are very poison- 
ous. All the cultivated sorts, radishes, 
beets, turnips, carrots, parsnips, chicory, 
etc., are natives of the old world. The 
last named, where cultivated, is chiefly 
used to make an adulterant for coffee, 
and has scarcely any nutritive 
value. 
American tubers are much more 
valuable. Indeed, the most valuable 
root crop in the world is the potato. Fic. 33. The poison hem- 
The potato crop stands among our feeciacnad eee 
crops second only to the wheat crop 
in cash value. And an acre of potatoes may produce as 
much human food as ten acres of wheat. The only other 
native tuber that is extensively cultivated is that of the arti- 
choke (Helianthus tuberosus) which maintains _ itself 
wild in great patches in many a rich bottomland thicket. 
The artichoke is able to win out over the other herbaceous 
perennials by reason of its sheer vegetative vigor: it over- 
tops them all and gets the sunlight. And when it blooms, it 
overspreads the thicket with a blaze of yellow sunflowers in 
late summer. There is another native tuber, however, of 
great promise: it has higher nutritive value than the potato 
and is very palatable; it is the so-calledgroundnut (Apios 
tuberosa). The plant is a vine, that grows in moist thickets 
and clambers over low bushes. It bears brownish purple, 
violet-scented, papilionaceous flowers in dense clustersin mid- 
summer. The tubers are borne on slender underground 
stems, often a number in a row, and are roundish or pear- 
shaped, very solid, and when cut, exude a milky juice, like a 
sweet potato. Doubtless, this valuable plant, which furnished 
the Indians with a dependable part of their living, 
