A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . 30 Figs. 30-32. — 30, A pod of wild vetch, with mature valves twisting spirally todischarge the seed ; 31, pod of cranes-bill discharging its seed ; 32, capsules of witch-hazel exploding. ig. Agencies of dispersal. — The means at natures dis-posal for this purpose, as show^n by the experiments just made,are four; namely, wind, water, the explosion of capsules dueto the withdrawal of water, and the agency of animals, in-cluding man. The first three are purely mechanical. The.

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