still exhibit, in the vascular elements of their 

 secondary wood, almost complete stages in the 

 transformation of scalariform pitting into 

 that of the circular multiseriate type, afford- 

 ing a valuable criterion by which to judge the 

 relative primitiveness of angiosperra groups. 

 The histologic evidence is fairly in accord 

 with the floral evidence. 



The exceptional abundance of circular pits 

 in such foirms as Vaccinium corymhosum, 

 noted by Jeffrey, is accentuated by the fact 

 that, in this type, the vessels are mostly 

 isolated from one another and in contact with 

 wood-prosenchyma which forms circular bord- 

 ered pits in common with the vessels. Sca- 

 lariform pitting occurs near the pith where, 

 occasionally, vessels are adjacent. Here occur 

 vessels showing perfectly the transition from 

 scalariform pits to scalariform perforations, 

 as well as the transition stages, noted by 

 Thompson,^ from scalariform to simple or 

 porus perforations. Forest B. H. Browx 



OsBOKN Botanical Laboratory, 

 Yale University 



-^Thompson, W. P., Jan., 1918, "Independent 

 Evolution of Vessels in Gnetales and Anglo- 

 sperms," Bot. Gas., LXV., pp. 89-90. 



