Un corso pratico in botanica : con particolare riferimento ai suoi cuscinetti su agricoltura, economia, e condizioni igieniche ., è chiaramente a vantaggio di una speciesche i suoi semi dovrebbero essere dispersi il più ampiamente possibile, per cui i giovani pianta possono avere molto spazio, e che theymay non deve trarre il loro nutrimento dal suolo alreadyesaured dai loro genitori. Il coltivatore riconosce questo principio nella rotazione ofcrops, perché sa chatsuccessivi crescite della pianta del thesame esauriranno presto il suolo delle sostanze i*e-quired per la sua nutrizione, whilethey può lasciarlo inno più ricco

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A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . conditions, it is clearly to the advantage of a speciesthat its seeds should be dispersed as widely as possible, boththat the seedlings may have plenty of room, and that theymay not have to draw their nourishment from soil alreadyexhausted by their parents. The farmer recognizes this principle in the rotation ofcrops, because he knows thatsuccessive growths of thesame plant will soon exhaustthe soil of the substances i*e-quired for its nutrition, whilethey may leave it richer innourishment for a differentcrop. 25. Self-planting seeds.—Dispersal is not the onlyproblem the seed has to meet.The majority of seeds cannotgerminate well on top of theground, and must depend onvarious agencies for gettingunder the soil. Some of themdo this for themselves. Theseeds of the storks-bill, popularly known as filarees, havea sharp-pointed base and an auger-shaped appendage at theapex, ending in a projecting arm (the clock of the filaree)by which it is blown about by the wind with a whirling motion. Fig. 45. — Self-planting pod of peanut. THE SKKD 27 till it strikes a soft spot, when it begins at once to bore itsway into the ground. The common peanut is another exam-ple. The blossoms are borne under the leaves, near the baseof the stem, and as soon as the seeds begin to form, theflower stalks lengthen several inches, carrying the young podsdown to the ground, where they bore into the soil and ripentheir seeds. Practical Questions 1. Name the ten most troublesome weeds of your neighborhood. 2. What natural means of dispersal have they ? 3. Which of them owe their propagation to man ? 4. Are there any tumbleweeds in your neighborhood ? 5. Would you expect to find such weeds in a hilly or a well-woodedregion? (19, 23; Exp. 17.) 6. What situations are best fitted for their propagation? (19, 23;Exp. 17.) 7. Make a list of all the fruits and seeds you can think of that ar

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• bookcentury1900
• bookdecade1910
• bookpublisher
• booksubjectplants