Lesson I. 

 CELL AND CELL DIVISION. 



(a) Plant Cells. 



Fruiii Olio lit till' layers of an onion remove with forceps a small 

 strip of the liim which covers its inner surface. Spread out tliis 

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

 glass. Use tlie low power. In stndyinii an unstained preparation, 

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

 thus cutting oli' all unnecessary light. 



Observe the large cells, oblong or nearly rectangular 

 ill 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 slij). In a few moments the cells 

 will assume a 3'ellowish-bro\vn 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 l.)een stained. 



(b) Karyokinesis in Plant Cells. 



Young and growing onion roots were hardened in Fieniing's '>vl/ 

 solution, embedded in parafhn, 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 deejDer than others. Examine these 

 under high power. Usualh^ 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 chromosomjjl can be clearly es / 



