[Reprinted from Science, N. S., Vol. XLVIIL, No. 

 1287, Pages 16-18, July 5, 1918] 



SCALARIFORM PITTING A PRIMITIVE 



FEATURE IN ANGIOSPERMOUS 



SECONDARY WOOD 



Professor Jeffrey, in his recent stimula- 

 ting book, " The Anatomy of Woody Plants," 

 Ch. VII., derives the vessel with the simple or 

 porous type of j)erforation from the fusion of 

 horizontal rows of circular pits in the end- 

 wall, the scalariforra pit and x)erforation be- 

 ing merely an intermediate stage in the proc- 

 ess. Perhaps such a reversible evolution has 

 gone on in certain groups, although it is here 

 attempted to show that the available evidence 

 is capable of the opposite interpretation. 



Multiperforate and even uniperforate end- 

 walls in gymnosi)ermous vessels may arise from 

 the fusion of circular pits with the dissolution 

 of the closing membrane as Professor Jeffrey 

 describes for Ephedra; but this fact seems 

 inadequate to explain either the presence of 

 scalariform pitting or the wide prevalence of 

 scalariform perforations in the vascular ele- 

 ments of the less specialized angiosperms. It 

 does not appear that all of the facts germane 

 to the subject have been fully considered. In 

 tracing out the development of vascular ele- 

 ments with imiperforated end-walls in accord- 

 ance with Jeffrey's hypothesis, serious diffi- 

 culty is met. 



The scalariform pits in conservative r^ions 

 of the secondary wood of Liriodendron, Drimys, 

 Asimina, and other forms with prevailing 

 circular pits in the less conservative r^ions, 

 suggest antecedence of the scalariform con- 

 dition, while a further illustration is afforded 

 by the monocotyledonous Dracaena. Thus, in 

 Draccena aurea, typical secondary xylem with- 



