712 



SCIENCE 



[N. S. Vol. XLI. No. 1063 



growth and the real question is: How can 

 the process of wounding induce growth in 

 cells which had been at rest and would 

 probably have remained so during the 

 whole term of life of the individual? It 

 is not the wound in itself which induces the 

 growth ; since in plants the growth of new 

 organs does as a rule not occur along the 

 area of the wound, but at some distance 

 where an old bud existed or a new one is 

 formed. The distance of the growing or 

 regenerating part from the wound may be 

 quite considerable.'' 



It has been stated that the isolation of 

 the parts is the cause of the new growth 

 following the wound. Thus if a leaf of the 

 tropical plant Bryophyllum calycinum is 

 cut off from the plant each of the notches 

 will give rise to a new plant when the leaf 

 is kept in a moist atmosphere. (This is the 

 regular way of propagating this plant.) 

 But no such growth will occur as long as 

 the leaf is kept in connection with the plant 

 (and the latter is normal). Here we seem 

 to have a clear proof of the generally ac- 

 cepted statement that isolation of parts 

 leads to regeneration. The idea seems to 

 be still further corroborated if we cut off 

 a leaf with a piece of the main stem of the 

 plant and suspend it in moist air. In this 

 case no new plants will grow from the 

 notches of the leaf. This again seemingly 

 supports the idea that the separation of the 

 part from the whole is the cause of growth 

 since the leaf attached to a piece of the stem 

 is less isolated than a leaf without any stem. 

 Yet it can be shown that if we diminish 

 the degree of isolation of the leaf still more 

 by leaving it attached to a stem stUl pos- 

 sessing the opposite leaf the power of the 

 first leaf to form new plants in its notches 

 is enhanced again. The experiment can be 



' The process of healing, i. e., of the closiag of 

 the wound, should be kept distinct from the phe- 

 nomena of growth which constitute regeneration. 



made in the following way. From the same 

 plant let be taken (1) an isolated leaf, (2) 

 a leaf with a piece of stem, (3) a leaf with 

 a piece of stem and the opposite leaf; let 

 all leaves be suspended in a moist chamber 

 with their tips submersed in water. The 

 first and third specimen will form new 

 plants in the submerged parts of their 

 leaves in a comparatively short time, while 

 the second will do so not at aU or consider- 

 ably later than the others.' Hence the ex- 

 periment shows first that complete isolation 

 induces the leaf to form new plants, that 

 less isolation will inhibit this phenomenon, 

 and that stiU less isolation will again call 

 forth the regeneration. It is therefore 

 plainly impossible to state that isolation is 

 the cause of regeneration. 



Those who make such a statement usu- 

 ally assume the existence of inhibiting in- 

 fluences in the plant and explain the effect 

 of isolation on regeneration or growth on 

 the assumption that the isolation frees the 

 part from this inhibiting influence of the 

 whole organism. We should be forced to 

 assume that in the normal Bryophyllum 

 there exists an inhibiting influence which 

 prevents the buds in the notches of the 

 leaves from growing, while when the leaf 

 is cut off the notches are released from this 

 inhibiting influence. To this idea we can 

 agree, but then the question arises : What is 

 this inhibiting influence ? Thus it is a com- 

 mon experience that in the isolated stem 

 of Bryophyllum only the apical buds will 

 grow, while if we cut off the apical buds the 

 next lower buds will grow out, and so on. 

 Hence the growth of the apical buds in- 

 hibits the growth of the lower buds. Some 

 more recent authors have suggested that 

 a kind of nervous influence is responsible 

 for this inhibition. But we have already 

 mentioned a niunber of facts which show 



8 A full account of these experiments on Bryo- 

 phyllum will be published in the Bear future. 



