:6 



DEVELOPMENT OF SIUM CICUTAEFOLIUM. 



borne only the closing members of the senescent series of leaf-forms 

 (fig. 3), were rejuvenated as a result of the submergence and made to 

 begin a new series, the early members of which show the most interest- 

 ing transitions from the senescent to the juvenile forms. Two of these 

 rejuvenations are shown in figs. 5 and 6. The two leaves (n 4, n 5) 



FIG. 6. Two rejuvenated buds from the upper portion of a stem of Sium cicutaefo- 

 lium: n 6 and n 4, leaves to which the buds were axillary. Numbers represent 

 the position of each leaf in the bud. Two thirds natural size. 



at the left in fig. 6 are the leaves to which the two rejuvenations shown 

 in the same figure were axillary. Unrejuvenated, the first leaf pro- 

 duced by each of these buds would have been a pinnate leaf of exactly 

 the same character as the leaf to which the bud was axillary, but with a 

 less number of leaflets. Instead of this we see in each case a leaf hav- 

 ing the same arrangement of parts, to be sure, but greatly modified in 



