REGENERATION IN PLANTS 7$ 



shown in Fig. 33, A, B. In this case leaf-buds appear at the apex of 

 the internodal piece (Fig. 33, A), even when the apical end is down- 

 ward (Fig. 33, B). From the bases of the new shoots roots may then 

 develop, as also shown in the figure (Fig. 33, B). Vochting con- 

 cludes that the same polarity that is a characteristic feature of longer 

 pieces is also present in internodal pieces. 



It is not necessary to separate completely portions of the stem in 

 order to produce roots near one end and shoots near the other. If a 

 ring, including the cambium layer, is cut from the piece, as indicated 

 in Fig. 32, C, the part above and the part below act independently of 

 each other, and each behaves as a separate piece. In various other 

 ways the same result may be obtained, as by simply making an 

 incision in the stem at one side, or by partially splitting off parts of 

 the stem (Fig. 34, C). 



If instead of a piece of the stem, a piece of a root is removed, 

 the results are as follows. 1 It should be remembered that the 

 basal end of a root is the part nearer the stem, the apex is 

 the part nearer the apex of the root. If pieces of the root of the 

 poplar, Populus dilatata, are suspended vertically (Fig. 32, D) in a 

 moist chamber, a covering of new cells, a callus, appears over the cut- 

 ends. From the basal callus numerous leaf-shoots may develop. 

 Pieces of large roots may produce over a hundred of these shoots 

 from a single basal callus. In some cases adventitious shoots 

 may also arise from the side of the root near the basal end. 

 Roots develop from the callus over the apical end ; less often from 

 the sides near the end. If a similar piece of root is suspended with 

 its apical end upward, the new shoots arise as before over the basal 

 end, that is now turned downwards. 



The leaves of some plants, as has long been known, are able to 

 produce new plants. The begonias are especially well suited for ex- 

 periments of this kind. A piece of the stalk of a leaf suspended in a 

 moist atmosphere produces roots near its base. In most cases the 

 opposite end of the stalk, i.e. the end nearest the leaf, putrefies and 

 slowly dies toward the base. Near the base there may arise, before 

 the breaking down of the piece has reached this point, leaf-buds that 

 arise just above the first-formed roots. When these new shoots have 

 reached a certain size they may produce their own roots at or near 

 the base. If, however, a portion of the leaf is left attached to the 

 leaf-stalk (Fig. 35, A), new roots arise near the basal end of the stalk, 

 and later shoots grow out near the point of union of the leaf and its 

 stalk at the point where the veins of the leaf come off. These shoots 

 produce roots of their own near the base, and roots may also appear 

 on the part of the leaf-stalk near its union with the lamina. If a 



1 Knight obtained similar results in 1809. 



