20 REMARKS ON THE DISTINCTIVE CHARACTERS 



which, however, the structure is the same, they are partly open, and partly 

 obstructed. There are seen in all, the medullary rays, and the oval aper- 

 tures of the great and smaller spiral vessels. These three sections are of 

 Dicotyledonous woods, similar to Fig. 3. 



Fig. 13. Sandal, or Sander Wood. This approaches in its characters 

 to the last three, but is remarkably compact in its texture, and has its layers 

 united, without any appearance of the lines of separation so apparent in 

 most of the rest. 



Fig. 14. Sugar Cane, Saccharum officinarum. Section of a portion 

 of the stem, shewing opaque spots of an oval form, being fasciculi of vessels, 

 generally presenting three apertures of larger spiral vessels ; the whole con- 

 tained in a uniform mass of cellular tissue or parenchyma. 



Fig. 15. Section of part of the stem of a species of Calamus, exhibiting 

 a similar arrangement. 



PLATE II. 



Transverse sections of Coniferae, although in themselves affording 

 very decided characters, by which trees of that family may be distinguished 

 from those of any other the structure of which has been examined are vet 

 insufficient as objects of comparison with those of fossil stems, for establish- 

 ing a generic identity in the two cases. A segment of the stem or branch 

 of a tree belonging to this family, presents the following structure. There 

 is a central cylinder of medullary cellules, which are of a roundish or irre- 

 gularly angular form. This cylinder is incased in a tube of woody or fi- 

 brous tissue, composed of cellules greatly elongated in a direction parallel to 

 the axis of the stem, and terminated by acute extremities. These cellules 

 are arranged in regular series, radiating from the medulla towards the cir- 

 cumference. Between them are interposed, at irregular intervals, series of 

 cellules, elongated in a direction perpendicular to the axis of the stem, and 

 forming thin plates parallel to the same axis. In a transverse section of the 

 stem, the elongated cellules of this woody tissue are seen to present series of 



