Quantitative experiments demonstrating the mechanism of the inhibition of growth

The problem of regeneration can also be stated in a negative way, namely: Why do tissues and dormant anlagen of organs not grow in an intact organism, while we know that they grow when the buds or tissues are isolated? The laws of inhibition were studied by a quantitative method.

No notch of a leaf of Bryophyllum will grow while the leaf is a part of the whole plant but the notches will grow when the leaf is isolated. When a leaf is subdivided into as many pieces as there are notches, each notch will give rise to a shoot; but if the leaf remains intact only few will grow out. The writer concluded that this again is a phenomenon of inhibition.

This inhibition he had explained in former papers 1 as being due to the fact that the inhibiting organ takes away the material required for the growth of the inhibited organ. If this were the case, we should expect that the total mass of shoots produced by a leaf in a certain time is approximately the same no matter whether the leaf produces few or numerous shoots. This is true to a surprising degree of exactness and the following numerical relations were established :

I. If a pair of sister leaves (of equal size) are isolated both will produce under equal conditions and in equal time approximately the same mass of shoots, although the number of shoots may differ considerably in the two sets of leaves.

2. If the mass of one of the two sets of sister leaves is diminished (by cutting out pieces of the leaves), the mass of shoots produced in the two sets is in proportion to the masses of the two sets of leaves.