110 THE CELL 



THE PLANT CELL. 



(2) Strip off the surface layer of cells from the piece of onion 

 scale provided. Examine and draw carefully under the high 

 power two or three of the cells, marking the parts. 



(3) I Tease out in a drop of water a little of the pulp of the 

 Snowberry, taking care that it is kept well wetted. Note that 

 the tissue is loose, with many air spaces between the cells, many 

 of which are spherical. Examine the cells under the high power. 

 Note that the proportion of cell sap to protoplasm in each cell is 

 very high. Look for the nucleus. Staining with dilute iodine 

 solution will often help in case of difficulty. 



(4) Examine the stained longitudinal section of the tip of a 

 bean root. Note that the actual tip is formed by the " root-cap." 

 The area just behind this is the " growing point " or primary 

 meristem, and consists of small mostly square cells densely filled 

 with protoplasm and with large conspicuous densely staining 

 nuclei. Draw carefully under the high power (a) examples of 

 meristematic cells with " resting nuclei," (b) different stages of 

 nuclear division * (compare with demonstration slides), (c) 

 different stages of vacuolation of the cells behind the meristem. 



Measure the diameter of a meristematic cell and of its nucleus, 

 also the length of one of the longest cells in the section. 



CELLS OF ANIMAL TISSUES. 



(5) Examine the demonstration specimens of stained and 

 mounted animal tissues. 3 Note cytoplasm, nucleus and absence 

 of cell wall : also, e.g. in cartilage, the intercellular substance 

 or " matrix." 



TURGIDITY AND PLASMOLYSIS. 



(6) Place one of the turgid bean roots (a) in 10 per cent. CaCl 2 

 solution, 4 leaving the other (b) on the table. After a few 

 minutes note that (a) has become quite limp. Place it in water, 

 and it gradually regains its turgidity; (b) gradually wilts as it 

 loses water by evaporation to the air. 



1 This may be omitted if the Practical Work is too long. 

 3 Demonstration slides under immersion objectives showing stages 

 in karyokinesis should be available if possible. 



3 Three or four slides will suffice : columnar epithelium, cartilage, 

 connective tissue and a preparation of muscle showing nuclei are 

 suggested as suitable. 



4 NaCl solution is liable to injure the protoplasmic membranes. 



