MICROSCOPIC OBJECTS. 



Fig. 13. Longitudinal Section of the Wood of the Elder 

 (Sambucus nigra), x 120, Exogen. 



This figure illustrates the longitudinal sections of the 

 medullary rays, as seen in situ. They appear as dark, oblong, 

 and pointed groups of cells in the mass of the ligneous or 

 woody tissue. It is these cells which give the rayed appear- 

 ance to transverse sections of the Dicotyledonous woods (see 

 Transverse and Longitudinal Sections of the various woods, 

 figs. 68, 69, &c.). The rays cross the annual circles existing 

 in the wood, and which indicate the age of the Dicotyledonous 

 trees. These cells generally become closer as they advance 

 in age. 



The object is best viewed in the dry state. 



Fig. 14. Longitudinal Section of American Pine (Pinus 

 Strobus), x 120, N. O. Coniferse. 



This section is used to illustrate the so-called glandular 

 tissue, which really consists, however, of pitted cells or 

 vessels. The cells are very numerous in this wood; and the 

 pits will be seen in each cell with a bordered outline, or, as it 

 is in reality, a slight concavity in the surrounding substance. 

 There are pitted ducts, as well as vessels, in other vegetable 

 structures (see fig. 8) . 



The cross lines in this figure represent portions of medul- 

 lary rays. 



The pits or dots on this tissue are often used to test the 

 quality of the object-glass of the microscope. When this is 

 good, they will appear free from colour. 



They are best seen in the dry state. 



