THE CHEMICAL MECIIAMSM OF REGENERATION 7 



of a hydrolytic process may be involved. By Ihus accelerating 

 the rate of shoot production in a notch we suppress at the same 

 time the grovvth ôf the other notches of the same leaf, inas- 

 miich as the available material in the leaf will now flow into 

 the growing shoot. How it happens that the material in the 

 leaf flows to that notch or those notches which by chance 

 first give rise to shoots can only be gnessed for the présent, 

 and may, therefore, be omilted from the discussion. 



The new shoots formed in the noiches may be considered as 

 parasites iiving on the leaf and fmally consuming it comple- 

 tely. In ail cells hydrolytic processes go on, until a definite 

 chemical equilibrium is reached between hydrolytic and syn- 

 thetic processes. The hydrolytic processes furnish Ihe amino- 

 acids, sugar, and other constituents needed for the growth of 

 roots and shoots from the notches. In two sister leaves thèse 

 hydrolytic processes will take place at the same rate as long 

 as the conditions remain alike, and from this we can under- 

 stand why in two sister leaves the production of shoots pro- 

 ceeds in proportion to the mass of the two leaves. It is pro- 

 bable that the assimilation in the leaf also contributes to the 

 quantity of material available for shoot production. This 

 seems to follow from the fact that in the dark the rate of 

 shoot production in a detached leaf is considerably diminished. 



II 



It had been observed by Wakker that when a pièce of stem 

 is left attached to a leaf of Bryophyllum calycinum the shoot 

 production in the leaf may be inhibited (fîg. 1) and the obser- 

 vation bas been confirmed by de Vries and by Gœbel. AVakker 

 attributed this inhibition to the « pressure » of the roots 

 formed on the pièce of stem, but it can be shown that the 

 inhibition takes place also when the root production is pre- 

 vented in such a pièce ot stem. Te suppression of shoot for- 

 mation in a leaf by a pièce of stem attache to it should fmd 

 its explanation on the same principle which was proved in the 

 first part ot this paper : namely, the withdrawal of the mate- 

 rial needed for régénération from the leaf by the stem. In 

 order to test this idea we again need quantitative methods. 



