200 APPENDIX. 



c. the nucleus suspended by strands of protoplasm in 

 the centre of the cell ; 



d. the nucleolus. 



[Staining with iodine or with eosin may be necessary 

 for c and d.] 



ii. Draw a drop of 5 / salt solution under the cover- 

 slip with blotting-paper. Note the shrinking of the 

 primordial utricle, i.e. the protoplasm lining the cell-wall, 

 as water passes from the large central vacuole by diffusion 

 into the salt solution. Having made a sketch of the 

 contracted cell, draw water through as before and observe 

 the cell reassume its turgid condition as the cell-sap 

 returns to its former volume. 



iii. Draw iodine-solution under the coverslip and note 

 that the light zone round the pyrenoids becomes nearly 

 black, which is due to the staining of the starch grains. 



III. Elder (Sambucus nigra). 



Cut a transverse section of a young stem of Elder, 

 keeping the razor wet. Stain for a few minutes in a small 

 quantity of iodine solution and mount in a drop of 

 Schulze's solution placed on a clean slide. Examine with 

 a low power, and note the pith in the centre and a similar 

 tissue (cortex) close to the periphery. Sketch a single 

 cell of the pith or cortex under high power, showing 



a. the cell- wall, stained blue (especially well seen in 

 the cortical cells) ; 



b. the primordial utricle, i.e. the protoplasm lining the 

 cell-wall : it is often somewhat shrunken away ; 



