BIOLOGY OF HIGHER SEED PLANTS 



25 



c. Cell-wall thickening. Focus with a high power on some 



thick-walled cells in the section. Observe the thick- 

 ness of the cell wall and the size of the cell cavity. 

 Are there intercellular spaces as in the thin-walled 

 pith cells ? Consult the text 

 concerning the mode of cell- 

 wall thickening (p. 48). 



d. Draw three or four thick- walled 



cells. 

 2. Vegetable fibers in paper. 



a. Examine pieces of filter paper 



and newspaper under the low 

 power of a compound micro- 

 scope. What appears to be the 

 composition of the paper ? Make 

 a rough sketch to indicate the 

 structure as it appears under 

 low power. 



b. Tease out a small piece of each 



kind of paper with needles in 

 a drop of water and mount 

 separately on the middle of a 

 glass slide. Cover with a cover 

 glass and study with both low 

 and high powers of the com- 

 pound microscope. What is the shape of these 

 vegetable fibers ? Have they a cell wall and a cell 

 cavity ? Compare them with the thick-walled cells 

 observed in celery. 



c. Draw two or three fibers accurately from each specimen 



examined and label their parts. Consult Fig. 10 of 

 these exercises. The fibers of which paper is made 

 resemble C in structure and in shape. 



ABC 



FIG. 10. Thick-walled 

 fibrous cells 



A, tracheid from pine 



wood ; B and C, fibrous 



cells 



