304 



QUANTITATIVE LAWS IN REGENERATION. I 



its regeneration had not been inhibited by the stem, but we can 

 determine this quantity indirectly, by measuring the quantity of 

 shoots and roots produced by the sister leaf detached from the stem, 

 since we know that two sister leaves of equal size produce equal 

 masses of shoots and roots in equal time and under equal conditions. 

 Our method of procedure was as follows. Pieces of stem possessing 

 one node with two healthy leaves of equal size were cut out (Fig. 4). 

 The stem was divided lengthwise as accurately as possible into two 

 equal pieces, h and bi, by a cut between the base of the petioles of 

 the two leaves, so that each leaf was connected with one-half piece 

 of stem of equal mass. One leaf (<Zi) remained in connection with 

 its piece of half stem {hi), while the other leaf {a) was detached from 

 its piece {h). The dry weight of this detached piece of half stem h 

 was determined immediately at the beginning of the experiment. 



Ill 



Fig. 4. Diagram to illustrate experiments in which the stem is cut lengthwise. 



At the end of the experiment the other piece of half stem hi was 

 detached from its leaf and its dry weight was determined. By 

 comparing the dry weight of hi with that of h (detached at the be- 

 ginning of the experiment) it was possible to ascertain how much 

 material the piece hi had received from the leaf during the time the 

 experiment lasted. Both leaves, the one detached from the stem as 

 well as the one left in connection with the stem, were suspended in a 

 moist aquarium, the apex of each leaf dipping in water. The de- 

 tached leaves formed shoots and roots very rapidly, while the leaves 

 in connection with their half pieces of stem formed practically no 

 shoots and roots.'* 



^ The inhibitory power of a piece of stem on the shoot formation in the leaf 

 increased within certain limits with the mass of the stem, but not in direct pro- 

 portion. It was also very obvious that equal masses of stem suppressed the 



