How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . ant. When the stem of a plantin vigorous growth is cut off nearthe root, and a pressure-gauge isattached to it as in fig. 43, wehave the means of observing andmeasuring the force with whichthe roots absorb water. The pres-sure-gauge contains a quantity ofmercury in the middle reservoir,b, and the tube, c. It is attachedto the stem of the plant, p, by astout india-rubber pipe, q.* Foraccurate measurements the space,a and 5, should be filled with warter. Thus arranged, it
How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . ant. When the stem of a plantin vigorous growth is cut off nearthe root, and a pressure-gauge isattached to it as in fig. 43, wehave the means of observing andmeasuring the force with whichthe roots absorb water. The pres-sure-gauge contains a quantity ofmercury in the middle reservoir,b, and the tube, c. It is attachedto the stem of the plant, p, by astout india-rubber pipe, q.* Foraccurate measurements the space,a and 5, should be filled with warter. Thus arranged, it is foundthat water will enter a throughthe stem, and the mercury wiUrise in the tube, e, until its pres-Fig. 43. sure becomes sufficient to balance the absorptive power of the roots. Hales, who first ex-perimented in this manner 140 years ago, found in oneinstance, that the pressure exerted on a gauge attached inspring-time to the stump of a grape vine, supported acolumn of mercury 32|- inches lijgh, which is equal to acolumn of water of 36^ ft. Hofmeister obtained on otherplants, rooted in pots, the following results:. * For experimenting on small plants, a simple tube of glass may be adjustedto the stomp vertically by help of a rubber connector. THE VEGETATTVB OEGAUS OF PLANTS. 249 Bean {Phaseolus rmdtiflorua) 6 inches of - - . - 14 « Vine ... - 29 Seat of Absorptive Force.—Dutrochet demonstratedthat this power resides in the surface of the young andactive roots. At least, he found that absorption was ex-erted with as much force when the gauge was applied tonear the lower extremity of a root, as when attached inthe vicinity of the stem. In fact, when other conditionsare alike, the column of liquid sustained by the roots of aplant is greater, the less the length of stem that remainsattached to them. The stem thus resists the rise of liquidin the plant. While the seat of absorptive power in the root lies nearthe -extremities, it appears from the experiments of
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectagricul, bookyear1868
