LESSON I. 

 CELL AND CELL DIVISION. 



(a) Plant Cells. 



From one of the layers of an onion remove with forceps a small 

 strip of the film which covers its inner surface. Spread out this 

 membrane on a slide in a drop of water, and cover with a cover 

 glass. Use the low power. In studying an unstained preparation, 

 it is best to employ one of the smaller openings in the diaphragm, 

 thus cutting off all unnecessary light. 



Observe the large cells, oblong or nearly rectangular 

 in shape, each surrounded by a distinct cell membrane. 

 Notice the round or oval nucleus with one or more nucleoli. 

 Carefully elevate the cover glass at one edge, and add a 

 drop or two of Lugol's solution or tincture of iodine, and 

 again replace the cover slip. In a few moments the cells 

 will assume a yellowish-brown color. Their structure can 

 now be made out more easily. Sketch a number of the 

 cells as seen under both low and high power, after they 

 have been stained. 



(b) Karyokinesis in Plant Cells. 



Young and growing onion roots were hardened in Fleming's 

 solution, embedded in paraffin, longitudinal sections cut and fixed 

 to cover glasses, and stained in safranin. Come .to the table with a 

 small drop of Canada balsam on your slide, and the section will be 

 mounted for you. 



Under the low power it will be noticed that some of 

 the nuclei are stained deeper than others. Examine these 

 under high power. Usually they will show some one of 

 the several stages of mitotic cell division. Observe the 

 difference in structure between a resting nucleus and one 

 in the spirem stage. In the former a chromatic network 

 will be seen, in the latter the chromosoma can be clearly 



