ILLUSTRATIVE STUDIES 89 



fragments will show what is wanted. Stain the sections in 

 fuchsin or safranin, dehydrate them in alcohol, rinse them in 

 xylene and mount them in balsam. 



4. Study cross sections of pine wood in dilute glycerine. Note 

 the absence of tracheal tubes and the presence of relatively large 

 tracheids in the early growth and small ones in the late growth. 

 Examine a longitudinal radial section and compare the tracheids 

 of the early and late growths. Draw a few tracheids from the 

 two regions from both points of view to show the relative sizes 

 of the tracheids and wall thicknesses. 



Macerate longitudinal sections in nitric aid and potassium 

 chlorate (page 312) and tease out the tracheids in dilute gly- 

 cerine. Draw to scale a tracheid from the early and the late 

 growths. 



Study in a similar manner wood of oak, walnut, and yellow 

 poplar. In both the macerated and unmacerated longitudinal 

 sections note the difference between wood fibers and fiber tra- 

 cheids, both similar in form, but the former with plain pits in 

 the walls and the latter with bordered pits (page 107). 



What does the microscopic examination show as the relative 

 hardness and lightness and uniform grain of these woods? 



In the longitudinal sections and macerations medullary rays 

 and wood parenchyma will be met with, and these should be 

 studied here enough to recognize their characters, although a 

 detailed study of them will be undertaken in another chapter. 



