49 EXPLANATION OF THE PLATES. 



Fie. 2. White Elm. The oblique and undulatory arrangement of the secondary pores of the 

 wood is a feature characteristic of the elms. Primary pores in a single row. The wood of 

 three yf'ars in contrast with which is the last annual layer of bnrk, which shows the perfect 

 regularity of the medullary rays, which are continuous with those of the wood. Old bark 

 corky and finely granular. 



Fig. 3. Bass-wood (Tilia americana). The structure of the bark is worthy of attention; the 

 medullary rays unite in the form of a pointed brush or pencil. 



Fio. 4. Pawpaw {Asimina triloba). The circle of primary pores single, and more distinct than 

 in the Bass-wood. The arrangement of the medullary rays of the bark is quite similar to 

 the bass. 



Fio. 5. Chinquapin Oak. Two sections cut transversely, and magnified about five times. The 

 striking difference of structure is manifest on comparing the oak with the chestnut (fig. 1). 

 All the small figures of Plate 8 indicate the size of the sections. 



PLATE 9. 



Fig. 1. Transverse section of a portion of two adjacent annual layers of the Poplar {Populus 

 tremttloides). Secondary pores belong to three kinds : the large, which are divided Jjy a 

 thin diaphragm ; the middle sized arc of a pentangular form, and are irregular in their 

 arrangement; the smallest contain dots or subordinate cells. 



Fig. 2. Section perpendicular to the medullary rays. 



Fig. 3. Section parallel to the medullary rays. 



Fio. 4. White Elder {Sambucus canadensis). Transverse section. 



Fig. 6. Section perpendicular to the medullary rays. 



Fio. 6. Section parallel to the medullary rays. 



Fig. 7. White-wgod {Liriodendron tulipifera). Transverse section. 



Figs. 8 & 9. Correspond with the former. 



PLATE 10. 



Fig. 1. Transverse section of the Walnut or Hickory. An interrupted single circle of large pore* 

 marks ihe commencement of growth of the wood. The interrupted belts indicate the direc- 

 tion of fine lines in the wood. The dark lines represent the medullary rays. 



Figs. 2 & 3. Sections perpendicular and parallel to the medullary rays. 



Fig. 4. White Oak [Quercus alba). Section transverse to the trunk shows, in the darker parallel 

 lines, the structure of the medullaiy rays. 



Fig. 6. Shows the structure of the same ray, when cut by a line tangent to its line of growth. 



Fig. 6. Section parallel to the medullary ray, showing its structure as brought out by this cut. 



Fig. 7. Black Oak. The three sections correspond to those of the White Oak. 



PLATE XL 

 CoNiFEBons WOODS. 1. Transverse section of White Cedar. 

 Figs. 4, 5, 6. Sections of the Red Cedar. 

 Figs. 7, 8, 9. Sections of the Norway Pine. 



The coniferous woods or pines exhibit a remarkable similarity of structure, as revealed 

 in these sections. Still there are differences worthy of note, and might be employed in 

 distinguishing species from each other. 



