STEUCTURE OP THE STEM. 



57 



oval figures, now show the whole length of the cell, and he 

 may study the way in which they interlock at the ends. 



In the radial section the medullary rays will frequently look 

 somewhat like portions of brickwork, as shown in Fig. 46. 



In the tangential section, only the 

 cut-off edges of the medullary rays will 

 be seen, as shown in Fig. 47. 



79. Separate Wood-Cells. — The com- 

 plete outline of wood-cells and bast-cells 

 Is most easily made out by examining 

 cells which have been separated from 

 each other by soaking wood or bark, as 

 the case may be, in a mixture of chlo- 

 rate of potash and nitric acid until it 

 can be easily picked to pieces in water 

 and viewed under the microscope. In 

 this way such cells as those shown in 

 Fig. 48 may be isolated and studied. 



80. Ducts of Various Fovms. — In 

 most of the hard-woods the ducts .are 

 poorly shown in the longitudinal sec- 

 tion, since they usually become much 

 split and broken in the process of cut- 

 ting the section. 



Study apd sketch some of the following, as 

 seen under a moderately high power : 



Eadiai longitudinal section of wood of tulip tree, longitudinal section 

 of stem of bracken fern (Pteris), stem of castor-oil plant (Fig. 49), of 

 peduncle of banana, or of root of chicory or licorice. 



81. Kinds of Tissue. — The student has now become 

 acquainted with a few of the many kinds of cells found in 

 plants, and has begun to see how they are grouped together 



1 The apparently vacant spaces at the ends of the lens-shaped sections of the 

 medullary rays are in most woods filled with cells, like the rest of the section. 



FiGr. 47. — Longitudinal Sec- 

 tion of Mahogany at right 

 angles to the Medullary 

 Bays, showing their cut- 

 off ends.i (Much magni- 

 fied.) 



