4SO BOTANICAL GAZETTE [june 



old stems the radial walls are considerably thicker. He showed 

 that each of these thick radial partitions is distinctly stratified, and 

 consists of a central cellulose septum, Zwischensubstanz, overlaid by 

 cellulose layers belonging to the protoplasts on either side of the 

 wall. Furthermore, he believed that at an early stage in the 

 development of tracheids thin spots appear in the radial primary 

 walls; and that, as the tracheids increase in size, these areas become 

 larger, the Zwischensubstanz is gradually absorbed, and the outer 

 layers of the wall are fused together and stretched to form a thin, 

 more or less homogeneous membrane. Inasmuch as bordered pits 

 are subsequently laid down over portions of these attenuated areas, 

 Sanio considered them to be Primordialtupfeln. He described 

 them as follows (p. 74) : 



Wahrend diese Verdiinnungen in der Membran seitlich. d. h., in horizon- 

 taler Richtung allmahlich in den starken verdickten Theil iibergehen grenzen 

 sie sich Oben und Unten scharf ab, und erscheinen hier sogar zuletzt mit dop- 

 pelten Umrissen. Haufig liegen diese Verdiinnungen so nahe an einander, 

 dass die sie trennenden verdickten Stellen als Querleisten erscheinen. Unter- 

 sucht man diese Bildung in Tangentialschnitte, so erscheinen diese Querleisten 

 als knotenformige Verdickungen der Membran zweier Nacharzellen, wahrend 

 die Verdiinnungen als zarte Scheidwande sich ausweisen. 



It is evident from Sanio's figures and descriptions that he 

 considered the primary pit areas, Primordialtupfeln , to be separated 

 by others in which the Zwischensubstanz is not entirely absorbed, 

 and in which the outer cellulose layers are less attenuated. It 

 should be emphasized, in this connection, that Sanio used the word 

 Querleisten, cross-pieces or cleats, in referring to transverse thicker 

 strips of the middle lamella between closely approximated primary 

 pit areas, and the word Umrissen, contours, in referring to the 

 upper and lower outlines of these areas. It is difficult to determine 

 with certainty whether Sanio understood the real significance of 

 the doppelten Umrissen, which partially surround the more isolated 

 primary pit areas in certain. of his drawings. That he probably 

 considered them to be contours, outlining the top and bottom of a 

 sloping surface or escarpment, is indicated by his illustration 

 (pi. 10, fig. 2) of a tangential section of a young tracheid of Pinus 

 silvestris. I have found no conclusive evidence in his text or figures 



