One of the most remarkable and important discoveries in connection with the regeneration of plants is that the new individuals that develop from leaves cut off from certain plants differ according to the region of the old plant from which the leaf has been taken. Sachs discovered in 1893 that when the leaves of the begonia are taken from a plant in bloom, the adventitious buds that develop from the leaves very quickly produce new flowers. If the leaves are taken from a plant that has not yet produced flowers, the new plant that develops from the leaf does not produce flowers until after a much longer time. Goebel repeated the experiment with achimenes, and found that the new plants that develop from leaves from the flowering part of the stem (Fig. 36) produce flowers sooner than do the plants that develop from leaves from the base of the same plant. The former produce, as a rule, only one or two leaves and the flower stalk; the latter, a large number of leaves. Sachs explains these results as due to a flower-forming stuff that is supposed to be present in the leaves when the plant is about to blossom. This material is supposed to act on the new plant that develops from the leaves, and to bring it sooner to maturity. Goebel points out that the result may also be explained by the fact that the leaves in the flowering region may be poorer in food materials and, in consequence, the adventitious buds that they produce are weaker, and, as experience has shown in other cases, a weakening of the tissues brings about more quickly the formation of flowers. Nevertheless, Goebel inclines to Sachs’ hypothesis of specific or formative stuffs, without, however, denying that there is also an inner polarity or “disposition” that also appears in the phenomena of regeneration. But Goebel seems to think that the phenomena of polarity “can most easily be brought under a common point of view by means of Sachs’ assumption that there are different kinds of stuffs that go to make the different organs. In the normal life of the plant shoot-forming stuffs are carried to the vegetative points, while root-forming materials go to the growing ends of the roots. In consequence, when a piece is cut off and the flow of the formative stuffs is interrupted, the root-forming stuff will accumulate at the base of the piece and the shoot-forming stuffs at the apex. In the leaf the flow of all formative substances is toward the base of the leaf, and it is in this region that the new plants arise after the removal of the leaf.” A confirmation of this point of view, Goebel believes, is furnished by the following cases. Some monocotyledonous plants seldom set seed because the vegetative organs, the bulbs, tubers, etc., that reproduce the plant, exert a stronger attraction upon the building stuff than do the young seeds.[35] Lindenmuth has shown in some of these forms that pieces of the stem produce, near the base, numerous bulblets, because the building stuff moves toward the base.