. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 78 PRACTICAL COURSE IN BOTANY ishment from the air, they are generally subsidiary to soil roots, like the long dangling cords that hang from some species of old grapevines; or they subserve other purposes altogether than absorbing nourishment, as the climbing roots of the trumpet vine and poison ivy. A very remark- able development of aerial roots takes place in the " stran- gling fig " of Mexico and Florida, which begins life as a small epiphyte, from seeds drop
. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 78 PRACTICAL COURSE IN BOTANY ishment from the air, they are generally subsidiary to soil roots, like the long dangling cords that hang from some species of old grapevines; or they subserve other purposes altogether than absorbing nourishment, as the climbing roots of the trumpet vine and poison ivy. A very remark- able development of aerial roots takes place in the " stran- gling fig " of Mexico and Florida, which begins life as a small epiphyte, from seeds dropped by birds on the boughs or trunks of trees. When it gets well started, the young plant sends down enormous aerial roots, which find their way to the ground, and in time so completely envelop the host that it is literally strangled to death (Plate 3, p. 73). When this support is removed, the sheathing roots take its place and become to all intents and purposes the stem of the fig tree, which now leads an independ- ent life. 89. The root system. — The entire mass of roots belonging to a plant, with all its rami- fications and subdivi- Fig. system of a tobacco plant. giong) composes a root system. The extent of root expansion is in general about equal to that of the crown, thus bringing the new and active parts under the drip of the boughs where the moisture is most abundant. Some plants have root systems out of all seeming proportion to their size. A catalpa seedling six months old showed, by actual measurement, 250 feet of root growth, and it is estimated that the roots of a thrifty cornstalk, if laid end to end, would extend a mile. In the development of the root system, a great deal depends upon external conditions. In a poor, dry soil, the roots have to travel farther in search of a livelihood, and so a larger system has to be developed than in a more favorable Please note that these images are extracted from scanned page images that may have been dig
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