DEVELOPMENT OF SIUM CICUTAEFOLIUM. 



19 



precocious than this, however, and all showed a much more rapid devel- 

 opment of the dissected form than is seen in the seedling. 



The simplest leaf presented by these proliferations (fig. 9) was a 

 minute oblong undivided structure which might be slightly widened 

 and flattened in the distal half, but otherwise showed no distinction of 

 blade and petiole. This might be followed by another undivided leaf 



Fig. 9.— Proliferations froni an inflorescence of Sium cicutaefolium. Numbers 

 show position of each leaf in its own proliferation. Variously magnlfled, x 6 to x 8. 



with a wider, elliptic blade. Then there might be a leaf having one or 

 a pair of simple lateral lobes, followed perhaps by the 5-lobed leaf or 

 the form which has been described as the simplest type of 3-lobed leaf 

 occurring in the seedling, having a 2-notched terminal lobe and bifid 

 lateral lobes. Whether the juvenile stages are atavistic or not, these 

 early leaves of the proliferations logically precede and lead up to them, 

 and carry us down the series to the siinplest possible type of leaf. 



