iqiqI bailey— bars of sanio 465 



siderable light upon a number of interesting problems, especially 

 upon the structure and true significance of the so-called rims or bars 

 of Sanio. 



Summary 



1. BandUke thickenings of the middle lamella and scalariform 

 primary pit areas are characteristic of tracheids which have scalari- 

 form bordered pits. They are widely distributed among the 

 Pteridophyta, G>Tnnospermae, and Angiospermae. 



2. The middle lamella frequently retains its typical scalariform 

 structure after the secondary wall has lost it. 



3. In the G>Tnnospermae, as well as in the Pteridophyta and 

 Angiospermae, there appear to be transitions between primary 

 membranes of this t\pe and others in which the scalariform 

 structure is profoundly modified, 



4. The comparative anatomy and ecology of the Pteridophyta, 

 Gj-mnospermae, and Angiospermae afford considerable evidence 

 which suggests that the tv-pes of unconformity and peculiar band- 

 like thickenings of the middle lamella (so-called bars or rims of 

 Sanio) which occur in certain Pteridophyta and Angiospermae, as 

 well as in many G>Tnnospermae, are concomitants of processes of 

 modification or reduction in tracheary pitting. 



5. The structure of the walls of the cambium and the develop- 

 ment of the pitting in the elements of the xylem and phloem in 

 Pteridophyta, G>Tnnospermae, and Angiospermae deserve more 

 careful consideration in discussions concerning the phylogenetic 

 significance of the so-called rims or bars of Sanio, than they have 

 received heretofore. 



BussEY Institution 

 Jamaica Plain, Mass. 



LITER.\TURE CITED 



Bary, a. de, Vergleichende Anatomic der Vegetationsorgane der Phanero- 

 gamen und Fame. Leipzig. 1877. 



Engler, a., and Gilg, E., Syllabus der Pflanzenfamilien. Berlin. 1912. 

 Gerry, Eloise, The distribution of the "Bars of Sanio " in the Coniferales. 

 Ann. Botany 24:119-123. 1910. 



