CHAPTER IV 

 REGENERATION IN PLANTS 



THE series of experiments that Vochting has carried out on the 

 regeneration of the higher plants are so much more complete than all 

 previous experiments, and his analysis of the problems concerning 

 the factors that influence regeneration is so much more exact than 

 any other attempts in this direction, that we may profitably confine 

 our attention largely to his results. Many of his experiments were 

 made with young twigs or shoots of the willow (salix), which, after 

 the removal of the leaves, were suspended in a glass jar containing 

 air saturated with water. Under these circumstances the pieces pro- 

 duced new shoots from the buds (leaf-buds) that are present near the 

 point at which the leaves were attached, and new roots, in part from 

 root-buds, that are also present on the stem. 



If the piece is suspended in a vertical position with its apex 

 upward (Fig. 32, A), small swellings appear after three or four days 

 near the lower, i.e. the basal, end of the piece. These break through 

 quickly and grow out as roots. If a leaf -bud is present near the 

 basal end of the piece, the first roots appear at the side of or under 

 this ; later others appear around the same region. The first roots 

 to appear under these conditions come from pre-formed root rudi- 

 ments, the others are, in part at least, new, adventitious roots. If 

 the lower end of the cut is made through the lower part of a long 

 internode, i.e. just above a bud, the roots appear as a rule only near 

 the cut-end, and few if any of the roots develop at the first bud above 

 this region. In many cases there is formed over the basal cut-surface, 

 in the region of the cambium, a thickening, or callus, and not infre- 

 quently from this also one or more roots may develop. The direction 

 taken 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 and 

 extent of development depending on the length of the piece. The 

 topmost or apical bud grows fastest, and the others grow in the order 

 of their position. In the region below the lowest bud that develops 



7' 



