DEVELOPMENT OF SIUM CICUTAEFOLIUM. 



17 



the direction of the tripartite leaf, which will be recalled as the modal 

 condition in the first nepionic leaf. In the second leaf in the one case 

 a form similarly transitional to the half-tripartite leaf occurred, and in 

 the other case the juvenile type of 3-loJ|pd leaf was perfected. With 

 the third leaf in the one rejuvenation and the fourth in the other, a pin- 

 nate form was produced which corresponded in every way with that 

 seen above to be the modal condition of the fifth nepionic leaf. This 

 was as far as one of these rejuvenations was followed. In the other 

 the fifth leaf had five pairs of leaflets, a degree of differentiation not 



Fig. 7.— Leaves of a rejuvenated bud from near the base of a stem of Sium cicutae- 

 /olium. Letters represent In a general way the position of each leaf In the reju- 

 venation; J/, an abnormally divided blade. Four-ninths natural size. 



usually attained during- the first year from seed. Later these rejuvena- 

 tions produced the dissected leaves characteristic of the autumn and 

 early spring growth. 



Lateral buds at the base of the flo\^(|ping stems are regularly rejuve- 

 nated in the autumn, and the first leaves are pinnate with one or several 

 pairs of undivided leaflets and are followed by a linear series leading 

 more or less quickly to the dissected condition (fig. 7) . It will be noted 

 that these basal rejuvenations never present leaves suggestive of the 

 earliest juvenile stages, as is the case in the rejuvenescence of buds 



