EXPLANATION OF THE PLATES. 49 



PLATE XII. 



Figs. 1, 2, 3. Button-wood (Platanus occidentalis). Sections corresponding to those already 



noticed. 

 Fig. 4. Beech. Transverse section. The dark belt shows the singular structure of the medullary 



ray. 

 Figs. 5 & 6. Sections of the same wood. 

 Fig. 7. Buckthorn. The oblong spaces which are left nearly white, are the spots thickly implanted 



with secondary pores. The wood is easily distinguished from all others by its singular 



structure. 

 Fig. 8. Cherry. 

 Fig. 9. Transverse section of the Plum. 



PLATE 13. 



Fig. 1. Melia azedarach. Section magnified four diameters, containing both bark and wood. 



Fig. 2. Section of the potato, showing its structure in a healthy state. The hexagonal cells con- 

 tain the starch granules. The spiral vessels are indicated by the three spirals upon the 

 right ; these vessels are always found in the vicinity of an eye. In a diseased potato, the 

 cells are broken down more or less, but the starch granules remain unchanged in the midst 

 of the decomposing fluids. These decomposing fluids contain the nitrogenous bodies, as 

 albumen and casein, which are at first acted upon, and which results in their decomposition, 

 as is evident from the exhalation of ammonia. Hence the nutritive powers of the diseased 

 potato are first diminished, while the calorifient power is the last to pass away. 



Fig. 3. Dogwood (Cornus fiorida). Medullary rays are remarkably continuous in this wood, 

 extending frequently from the centre to the circumference. 



Fig. 4. High Blackberry (Rubus villosus). Transverse section of the stem. 



Fig. 6. Baspberry. From comparison of the structure of the two stems, it would seem expedient 

 to separate the High Blackberry from the Raspberry. 



Fig. 7. Transverse section of Black Ash. 



Fig. 8. Transverse section of White Birch. 



Fig. 9. Transverse section of the Black Birch (Betula excelsa). It appears, from the structure of 

 the stems of the several species of birch, that they are more closely allied than many other 

 species. So close is the resemblance, that it is extremely difficult to distinguish them : the 

 resemblance, in fact, is greater than in two species of the Pine. 



PLATE 14. 

 Fig. 1. Transverse section of the Canada Balsam. 



Fig. 2. Section parallel to the medullary rays, showing the dotted tissue in a medullary ray. 

 Fig. 3. Section perpendicular to the medullary rays. 

 Fig. 4. Transverse section of the Tamarack. 



Fig. 5. Transverse section of Hemlock, magnified about five diameters. 

 Fig. 6. Transverse section of Hemlock, greatly magnified. 

 Fig. 7. Section of the White Elm parallel to the medullary rays, showing the spiral vessels of 



the wood. 

 Fig. 8. Transverse section of the Taxus. 

 Fig. 9. Transverse section of the White Elm. 



