766 DIKECTIONS FOE LABORATORY WORK 



II. THE CELL 



(A) THE PLANT CELL. 



(1) Mount in water a small piece of the membrane separating the 

 inner layers (leaves) of an onion. Note shape and size of cells, manner 

 in which the cells are grouped, location and relative size of nucleus, 

 nucleoli, cell wall, and character and contents of the cytoplasm. Identify 

 the rod-shaped mitochondria. 



Make l.p. sketch (6) of a small group of cells; and h.p. sketch (7) 

 of a single cell. Compare with section of cork. Difference ? Propriety 

 of name 'cell' ? 



(2) Make similar preparation, study and sketches (8, 9) of a thin 

 slice of the onion leaf. Identify an air globule. 



(3) Mount in water a -thin slice of the potato. Sketch (10) under 

 h.p. a cell, noting carefully the nucleus and the starch grains. Make 

 careful sketch (11) of a large starch grain. Add a drop of tincture of 

 iodine, and note the color change of the starch grains ; and observe again 

 the shape, size and location of the nucleus. 



(4) Examine small portion of the leaf of a common higher moss 

 (e.g., Bryum), and sketch h.p. (12) a cell, noting especially its robust 

 CELL WALL, and its content of chlorophyll bodies (chloroplasts). 



(B) THE ANIMAL CELL. 



(1) Scrape gently with finger inner surface of cheek and mount the 

 debris. Note the greatly flattened plate-like cells (squamous cells). 

 Make l.p. sketch (13) of a small group; h.p. sketch (14) of a typical 

 isolated cell. 



(2) OVUM (egg cell). Make a careful drawing (15) (from demon- 

 stration slide of starfish ovary) of a large egg. Note endoplasm, exo- 

 plasm, cell membrane, and nuclear membrane. In the cytoplasm ob- 

 serve spongioplasm, hyaloplasm, microsomes; in the nucleus, chromatin, 

 nucleolus, linin, chromioles, and karyosomes. Character of cytoplasm? 



\3) Sketch (16, a) cell with mitochondria (demonstration slide); 

 (16, b) cell with ergastoplasmic fibrils (e.g., acinar cell of pancreas, or 

 lining entodermal cell of yolk-sac of 10 mm. pig embryo). 



(4) Sketch (17) astral system (demonstration slide of maturing 

 or segmenting egg of some invertebrate, e.g., starfish, clam). Note cen- 

 trosome, centriole, centrosphere, astrosphere, and achromatic spindle. 



