ECONOMIC WOODS OF THE UNITED STATES 



TABLE VII 



135 



INDIGENOUS WOODS WITH VESSEL PERFORATIONS EXCLUSIVELY OR PRE- 

 DOMINANTLY SIMPLE 



* With some tendency to scalariform, particularly in the region of primary wood. 



Scalariform perforations look like a grid-iron or grating with an 

 elliptical or elongated-elliptical contour. The bars, with very 

 rare exceptions, are arranged horizontally or transversely. As 

 the plane is almost invariably strongly oblique and facing the ray, 

 the structure is seen to much better advantage in radial sections 

 than in the transverse and tangential. Macerated material is 

 better still since a portion of the tilted plate is likely to be cut off 

 in sectioning. Bars may also be seen in the lumina of some of the 

 vessels in the transverse section, especially if the section is rather 

 thick. 



The number of bars in a perforation varies from very few to 



