THE CELL AS A MEMBER OF A GROUP. 39 



In the latter it generally forms a central pith, con- 

 nected with the bark by more or less developed 



Fig. 14f 



portions of cellular tissue, 

 called the medullary rays. 

 (Figs. 14 and 14^.) 



10. These various ele- 

 ments of plants, consisting 

 of different forms of cells, 

 tissues, and fibro-vascular bundles, are arranged in 

 each species in a characteristic manner, so that it is 

 often possible to recognize the species from a small 

 fragment of the plant. For this purpose small trans- 

 parent sections of a stem are prepared, cut in three 

 different ways transversely, longitudinally through 

 the center, and a section parallel to the last. These 

 are mounted on glass slips, three inches long by one 

 wide, saturated with Canada balsam or other preserv- 

 ative fluid, and covered with very thin glass for 

 microscopic examination. 



