. Foundations of botany. -4^^ f Fig. 15. — Aerial Adventitious Koots of tlie Ivy. roots, or haustoria, form the most intimate connectionswith the interior portions of the stem or the root, as thecase may be, of the host-plant on which the parasitefastens itself. In the dodder, as is shown in Fig. 16, it is most inter-esting to notice how admirably the seedling parasite isadapted to the conditions under which it is to live. Kooted 1 See Kerner and Olivers Natural History of Plants, Vol. I, pp. 171-213. 40 FOUNDATIONS OF BOTANY at first in the ground, it develops a slender, leafless stem,which,
. Foundations of botany. -4^^ f Fig. 15. — Aerial Adventitious Koots of tlie Ivy. roots, or haustoria, form the most intimate connectionswith the interior portions of the stem or the root, as thecase may be, of the host-plant on which the parasitefastens itself. In the dodder, as is shown in Fig. 16, it is most inter-esting to notice how admirably the seedling parasite isadapted to the conditions under which it is to live. Kooted 1 See Kerner and Olivers Natural History of Plants, Vol. I, pp. 171-213. 40 FOUNDATIONS OF BOTANY at first in the ground, it develops a slender, leafless stem,which, leaning this way and that, no sooner comes into. ;j///;?///// -? ABC • Fig. 16. — Dodder, growing upon a Golden-Rod Stem. s, seedling dodder plants, growing in earth; h, stem of host; r, haustoria orparasitic roots of dodder ; I, scale-like leaves. A, magnified section of a por-tion of willow stem, showing penetration of haustoria. permanent contact with a congenial host than it produceshaustoria at many points, gives up further growth in its ROOTS 41 soil-roots, and grows rapidly on the strength of the sup-plies of ready-made sap which it obtains from the host. 52. Forms of Roots. — The primary root is that whichproceeds like a downward prolongation directly from thelower end of the hypocotyl. In many cases the mature root-system of the plant contains one main root much largerthan any of its branches. This is called a taproot (Fig. 17). Such a root, if much thickened, would assume the form
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