Un cours pratique dans la botanique : avec une référence particulière à ses roulements sur l'agriculture, l'économie, et l'assainissement . rass, mayweed et bitterweed, possèdent des moyens naturels veryimparfaits de dispersion, et sont largement tributaires de leur propagation sur l'agence involontaire de l'homme.23. Utilisation du fruit dans la dispersion. — Il sera vu à partir des observations qui précèdent que le fruit joue un très important dans le travail de dispersion, mostof des adapta-tions pour ce pur-pose étant con-nected avec lui.Dans les cas où le anubre de plantules sont conteneueddans un grand podopqui pourrait notoirement se belapler autour de bythe

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A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . rass, mayweed and bitterweed, possess veryimperfect natural means of dispersal, and are largely depend-ent for their propagation on the involuntary agency of man.23. Use of the fruit in dispersal. — It will be seen from theforegoing observations that the fruit plays a very importantpart in the workof dispersal, mostof the adapta-tions for this pur-pose being con-nected with it.In cases where anumber of seedsare containedin a large podthat could notconveniently beblown about bythe breeze, adaptations for wind dispersal are attached to the individual seeds, as in thewillow, milkweed, trumpet creeper, and paulonia; but as ageneral thing, adaptations of the seed are for protection, thework of dispersal being provided for by the fruit. In the caseof the large class of plants known as tumbleweeds, thewhole plant body is fitted to assist in the work of transporta-tion. Such plants generally grow in light soils and eitherhave very light root systems, or are easily broken from their .ir.i ^. Fig. 43. —A fruiting plant ofwinged pigweed {Cycloloma), showing the bunchy top and Fig. 44. — Panicle otweak anchorage of a typical old witch grass, a coni-tumbleweed. mon tumbleweed. 26 PRACTICAL COURSE IN BOTANY anchorage and left to drift about on the ground. The spread-ing, bushy tops become very light after fruiting, so as to beeasily blown about by the wind, dropping their seeds as theygo, until they finally get stranded in ditches and fence corners, where they often accumulate in great numbers during theautumn and winter. 24. The advantages of dispersal. — Seed cannot germinateunless they are placed in a suitable location as to soil, moisture, and temperature. In order to increase the chances of secur-ing these 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

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