PLATE 4. EXOGENOUS STRUCTURE IN WOOD. 

 (CROSS-SECTIONS, ENLARGED.) 



Two yearly layers of White Oak. The larger pores were formed in spring, the 

 smaller ones in summer. The small circles are ends of fibres. A knife pressed 

 upon this surface would crush or cut into the cells. The mass would not split or 

 separate evenly. 



Two yearly layers of White Pine. The space in the outer or darker one is a 

 resin-duct; the circles are ends of fibres (tracheids); pith rays are noticeable. A 

 knife pressed upon this surface would find easy passage. The mass would separate 

 easily. 



