DEVELOPMENT OF SIUM CICUTAEFOLIUM. 



II 



Burns (1904) has recently demonstrated a similar independence from 

 aquatic conditions, in the dissected leaf of Proserpinaca palustris, 

 though McCallum ( 1902) had looked upon it as a direct response to the 

 dilution of the protoplasm brought about by the abundance of water and 

 the stoppage of transpiration. Burns considers the dissected leaf of 

 Proserpinaca as a juvenile type, but this is certainly not the case in 

 Sinm cicutae folium. 



A more pronounced, even extreme, dissection of the leaves character- 

 izes the resumption of growth in the spring (Plates I and VII), so that 



FIG. 2. Autumnal modification of leaves in the seedlings of 

 Sium cicutaefolium. Numbers represent the position of each 

 leaf in the series, beginning with the first nepionic leaf. 

 Three-fourths natural size. 



in so far as this region indicates the ancestry of the species the ancient 

 Siums should have resembled a fennel (Poeniculum} or a parsley (Lo- 

 matium}. These dissected leaves are rarely seen by the systematist who 

 works only with pressed material, as one may convince himself by look- 

 ing through the specimens of Sium in any large hrebarium. Of more 

 than 100 specimens of this genus in the herbarium of the New York 

 Botanical Garden not one showed these dissected leaves. The change 

 from dissected leaves to the simply pinnate leaves with linear, lanceolate 



