. A textbook of botany for colleges and universities ... Botany. 510 ECOLOGY root to a plant. Thus the modifications induced when soil roots are grown in water (viz. reduction in size and in hair production) are seen to be the usual features in aquatic roots. The cause of reduction and of hairlessness in water roots is unknown, though it is likely that the conclusions reached in the case of soil roots are applicable here. In some water plants, as Ceratophyllum, Utricularia, and Salvinia (fig. 897), roots are wanting and absorption is confined to the leaves and stems. The duckweeds may have sev
. A textbook of botany for colleges and universities ... Botany. 510 ECOLOGY root to a plant. Thus the modifications induced when soil roots are grown in water (viz. reduction in size and in hair production) are seen to be the usual features in aquatic roots. The cause of reduction and of hairlessness in water roots is unknown, though it is likely that the conclusions reached in the case of soil roots are applicable here. In some water plants, as Ceratophyllum, Utricularia, and Salvinia (fig. 897), roots are wanting and absorption is confined to the leaves and stems. The duckweeds may have sev- eral roots (as in Spirodela), one root (as in Lemna), or no root (as in Wolffia); in all three there is a thallus rather than a leafy stem, and in the rootless Wolffia, absorption takes place in the same manner as in the algae. In water roots the outer layers do not become impermeable with age, so that absorption takes place through the entire surface instead of through the tips, only, as in soil roots. Water roots are of no value as anchorage organs, but they may assist in the maintenance of equilibrium. Many aquatic roots contain chlorophyll, and it may be that food manufacture is an accessory r61e of some importance. An interesting feature of water roots is the root pocket, a structure that fits over the root tip like a glove finger (fig. 728). Although root pockets are much more conspicuous than are the root caps of soil roots, their advantage to the plant is less evident. Roots intermediate between soil and water roots are found in various attached aquatics, such as Elodea and Myriophyllum. Horizontal branches give rise to hairless unbranched roots Fig. 728.—The tip of ii water root of a water hyacinth (Eich- hornia spsciosa), show- ing the root pocket, which tits over the root like a glove finger; considerably magni- Fig. 729.—A tropical epiphytic orchid {Epidendrum ramosuni), showing aerial ab- sorptive roots arising adventitiously from the nodes, and mostly
Size: 1229px × 2032px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
