112 



REGENERATION 



where the small piece of stem with a leaf near the base forms 

 considerable callus while the large piece of stem with the leaf at 

 a greater distance has in the same time formed almost no callus 

 (Nov. 30 to Dec. 14). It is also shown in Fig. 87, where a piece 

 of stem with a pair of sister leaves at the apex was split longi- 

 tudinally. The greater part of one half 

 stem was cut off in one piece. In the 

 latter piece, where the leaf was nearer 

 the base (to the left in Fig. 87), the 

 callus formation at the base of the stem 

 was considerable while the long piece 

 had not yet formed any callus. A 

 small callus was formed later. 



We have seen that the inhibitory 

 effect of an apical leaf on shoot forma- 

 tion in a stem suspended vertically and 

 upright is greater when the stem is 

 young than when it is old. It is of 

 interest that the callus formation in old 

 stems is also less than in young stems. 



All these experiments show the par- 

 allelism between the effect of the apical 

 leaf on callus formation and on the 

 inhibition of shoot formation in the basal 

 part of the stem. 



Figure 88 shows the inverse relation 

 between callus formation and shoot for- 

 mation in the basal part of a leaf. The 

 stem in Fig. 88 has a large leaf at the 

 apex which dips into water. In the node 

 below the apex one shoot is formed, 

 while on the other side of the same node 

 none is formed. Only one half of the 

 base of the stem has formed a callus; namely, where there is no 

 shoot; the other half of the base of the stem has formed none, 

 for the reason that here a thickening has occurred in the region 

 of the new shoot and that the material was consumed here which 

 otherwise might have served for callus formation at the base. 

 The same correlation is shown in Fig. 89. Young stems with 

 a large apical leaf with only one node below the apical one and 

 with the shoot opposite the leaf removed, form no shoots in the 



Fig. 88. — Callus formed 

 only on that side of the stem 

 where no shoot is formed. 



