Regeneration . not infre-quently from this also one or more roots may develop. The directiontaken by the new roots is variable, being sometimes downward,sometimes more or less nearly at right angles to the stem. While these changes have been taking place at the base, the leaf-buds at the apical end have begun to develop. One, two, three, four,or even five of the higher buds begin to elongate, the number andextent of development depending on the length of the piece. Thetopmost or apical bud grows fastest, and the others grow in the orderof their position. In the region below the lowest bud that
Regeneration . not infre-quently from this also one or more roots may develop. The directiontaken by the new roots is variable, being sometimes downward,sometimes more or less nearly at right angles to the stem. While these changes have been taking place at the base, the leaf-buds at the apical end have begun to develop. One, two, three, four,or even five of the higher buds begin to elongate, the number andextent of development depending on the length of the piece. Thetopmost or apical bud grows fastest, and the others grow in the orderof their position. In the region below the lowest bud that develops 71 72 REGENERATION there may be one or more buds that do not grow; but if the piece iscut in two just above these buds, they will then grow out. The results show that at the base of the piece the same factorsthat bring about the development of the rudiments of preexistingroots also cause the development of new roots, if the lower end isin a region in which there are no rudiments of roots present. The. Fig. 32. — After Vochtin?. A. Piece of willow cut off in July, suspended in moist atmosphere withapex upward. B. Older piece of willow (cut off in March) suspended in moist atmospherewith apex downward. C. Piece of willow with a ring removed from middle. Apex upward. D. Piece of root of Populus dilatata. Basal end upward. Shoots from basal callus. E. Piece of root of same with two rings removed. New shoots develop from basal callus,and from basal end of each ring. influence that produces the new roots is confined to the basal partof the piece. In the apical part of the piece there are no adventi-tious structures produced, but a longer region is active, and severalpre-formed leaf-buds begin to elongate. The topmost shoot growsfaster than the others, showing that the influence that produces thegrowth is stronger near the apical end than at points further another piece of a willow stem be placed under the same condi- REGENERATION IN PLANTS 73 tions, but suspend
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