MICROSCOPIC OBJECTS. 34 



Fig. 67. Transverse Section of the Wood of the Willow 

 (Salixalba), x 120. Exogen. 



The transverse section of this wood shows the very large 

 number of ducts that the wood contains. The smaller holes 

 represent the transverse sections of the ordinary prosenchy- 

 matous cells,, and the dark lines represent the transverse 

 sections of the medullary cells. As was mentioned at fig. 66, 

 this wood is remarkable for its extreme elasticity, the cause 

 of which is evident on referring to the drawing; the ducts 

 being numerous and large, allow for the extra pressure of the 

 prosenchymatous, or woody fibre, when the wood is bent. 

 Both the ducts and the woody fibre are also greatly strength- 

 ened by the small yet strong and frequently occurring medul- 

 lary cells. 



Fig. 68. Longitudinal Section of Norfolk-Island Pine 

 (Araucaria excelsa), x 120. N. O. Coniferse. 



This wood has been chosen chiefly to illustrate that of the 

 N. O. Coniferse, which, unlike most other woods, is destitute 

 of the ducts. The transverse sections of the prosenchymatous 

 cells are generally of an hexagonal form ; while the longitu- 

 dinal sections exhibit, under a moderate power, glands or pits 

 seated in the prosenchymatous or woody cells, as shown in 

 fig. 14. The large holes in the drawing of this wood repre- 

 sent the transverse sections of the medullary cells. 



Many of the cuticles of the leaves of the Coniferse exhibit 

 interesting structures, an instance of which was shown in 

 fig. 24. 



