MICROSCOPIC OBJECTS. 30 



Fig. 59. Transverse Section of Bauhinia (Bauhinia chinen- 

 sis), x20. N. O. Leguminosae, Exogen. 



Exogenous are distinguished from endogenous plants by 

 having a bark, concentric annual growths of wood, and a 

 pith in the centre, also for having medullary rays or cells 

 proceeding from the pith to the bark. The bark, wood, pith, 

 &c. will be seen in this drawing ; and for a description of an 

 endogenous stem see fig. 72. Prosenchymatous cells, form- 

 ing woody tissue, are in greater abundance in the Exogens 

 than in the Endogens ; but the former contain less vascular 

 and cellular tissue than the Endogens. 



Wood-sections are best seen when mounted dry, although 

 Canada balsam may often be used with advantage. 



Fig. 60. Longitudinal Section of the Wood of the Cork-Oak 

 Tree (Quercus Suber), x 50. Exogen. 



The ducts of this wood seem to be extremely large, and 

 the prosenchymatous or woody cells rather more closely con- 

 nected than in most woods. The wood of this species of Oak 

 has a thick bark, which is largely used in commerce under 

 the name of cork. This bark is composed of extremely 

 small and at the same time closely packed cells of cellular 

 tissue, which tends to give that fine elastic quality which 

 makes it so useful an article where these qualities are so 

 greatly needed. 



