CHAPTER VI 



WHY DOES SEPARATION OF A LEAF FROM THE PLANT 

 INDUCE THE GROWTH OF ROOTS AND SHOOTS 



IN THE LEAF? 



We now come to the main problem of regeneration; namely, 

 why mutilation leads to growth which would not have occurred 

 without mutilation. In the case of the leaf of Bryophyllum, the 

 question arises : Why does the leaf form new shoots and roots in 

 its notches only when it is detached from the plant, but does not 

 do so when connected with the plant? The quantitative method 

 permits us to give a definite answer: that as long as the leaf 

 is connected with the stem of a normal plant, the material 

 formed under the influence of light in the leaf goes into the stem 

 and causes growth of the stem as well as growth of shoots at the 

 apex and of roots at the base of the stem. 



It is not necessary that the leaf should be connected with a 

 whole plant in order to inhibit the formation of shoots in the leaf. 

 The inhibition of regeneration in a leaf is already noticeable when 

 the leaf is attached to a small piece of stem. 



Figure 27 represents a pair of sister leaves, one detached, the 

 other in connection with a small piece of stem. Each leaf dips 

 with its apex into water. The leaf without stem has formed four 

 large shoots and roots, while the sister leaf, which is attached to 

 a piece of stem, has just commenced to produce a tiny shoot. 



The same inhibition can be demonstrated still more strikingly 

 when the two leaves are suspended entirely in moist air (Fig. 28) 

 (instead of dipping into water). The one leaf without stem had 

 formed three shoots in notches, while no regeneration occurred in 

 the sister leaf which remained in connection with a piece of stem. 

 The small piece of stem suppressed all shoot and root formation 

 in the leaf; but a shoot was formed on the stem in the axil of the 

 leaf. The stem inhibited the shoot formation in the leaf because 

 the material for regeneration went into the stem. These two 

 leaves had the red pigment (anthocyanin?) which substance 

 makes it possible to follow the path of migration of material. 



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