Section V, 1922 [83] Trans. R.S.C. 



XV. The Bar of Sanio and Primordial Pit in the Gyrïinosperms 



By H. B. SiFTON, M.A. 

 (Read May Meeting, 1922) 



Sanio's well-known investigation of the development of the 

 secondary tissues in the Scotch Pine contains the first attempt at 

 critical study of the structures to be considered in this paper. Using 

 material which had been freed of protoplasm by heating with acetic 

 acid, he noted that the cambium cells and the very slightly enlarged 

 cells adjacent to them on the side of the wood are provided with 

 smooth walls of even thickness. Before these wood elements have 

 reached their full size, however, rounded, thin places are observed 

 to form on their walls, and these thin spots enlarge with the growth 

 of the cells. Sanio notes that while horizontally these primordial 

 pits shade ofif gradually into the thicker portion of the cell wall, the 

 edges above and below are sharply delimited, appearing when mature 

 with "doppelten Umrissen." Since the time of Sanio's publication 

 improved methods of staining have shown that the "double rims" 

 which he observed were merely the edges of a newly developed 

 structure, a thickening in the primary wall of the cell forming a curved 

 ridge above or below the primordial pit. To these ridges the name 

 "Rims of Sanio" has been applied. Where the pits approximate 

 the adjacent rims fuse, taking the form of "Querleisten," the so-called 

 "Bars of Sanio." As seen in tangential section, Sanio refers to these 

 bars as " knotenformige Verdickungen der Membran zweier Nach- 

 barzellen." On the thinned spaces, or primordial pits, the bordered 

 pits of the secondary wall are formed. 



Until the year 1910 very little attention was paid to bars of 

 Sanio, but in that year a paper on their distribution by Miss Gerry (2) 

 aroused a great deal of interest among those engaged in the study 

 of conifers, especially those interested in fossil forms. A paragraph 

 from her conclusions will illustrate the value attached by her to the 

 rims of Sanio: 



The distribution of the bars of Sanio above described establishes a constant and 

 useful diagnostic character in the determination of fossil woods. In woods with 

 Abietineous affinities we always find bars of Sanio even though at the same time we 

 may find more or less Araucarian-like pitting. But in the Araucarineae we never 

 find bars, although in fossil forms such as the Araucariopityoideae and the Brachy- 

 phylloideae, we find Abietineous as well as Araucarian pitting. 



