7 To demonstrate osmosis: Temporarily seal the small end of a thistle tube 

 and fill the bulb with granulated sugar. Pour as much ink or colored water as pos- 

 sible on the sugar in the bulb. Tie a moist bladder or sausage-casing membrane 

 firmly in place over the large end with about twenty turns of thread. Invert the 

 thistle tube, attach a long glass tube to the open end with a piece of rubber tubing, 

 and place bulb in a jar of water. 



Hollow out the thick end of a large carrot (use apple-corer if convenient) and 

 partially fill the space with sugar and ink; seal a glass tube in the open end of the 

 carrot with a one-hole rubber stopper. Keep top of carrot dry during this sealing 

 process. The outside may be reinforced by wrapping with friction tape; the top 

 may be sealed with candle wax or paraffin. Submerge the carrot in a jar of water. 



Record results in both cases and account for them. 



8 To show how water can furnish mechanical support by filling the cells 

 and tissue and stretching the outer membranes: 



Prepare two widemouthed bottles to represent cells, as shown in illustration 

 on page 88; fill one with a concentrated salt or sugar solution and the other with 

 pure water; tie an "osmotic" membrane securely over the top of each; submerge 

 the one containing the sugar or salt in a pan of water and the other in a pan of 

 water containing salt or sugar solution. Compare the behavior of the two mem- 

 branes and show wherein one of the model cells represents the condition found in 

 the cells of wilted celery, the other in fresh celery. 



Cut fresh rhubarb stalks squarely at one end; then peel down a narrow strip 

 nearly the full length from the cut end; place the peeled portion back along the 

 cut surface and note that the two no longer match. Split dandelion stems length- 

 wise; note how they curl. Place some of the split stems in fresh water and others 

 in salt water. Record results in each case and explain how they came about. 



Cut four thin slices each of carrot, turnip and potato. Place one slice of each in 

 fresh water, one in a salt solution, one in a saturated sugar solution, and one in air. 

 The following day note the differences among the slices and account for them. 



, Water one pot of rapidly growing seedlings (corn, oats, or wheat) with a 

 saturated salt solution and another with tap water. After a few days compare the 

 behavior of the plants in the two pots and account for the differences. 



QUESTIONS 



1 What conditions are essential for the germination of seeds? 



2 In what respects are the chemical processes which go on inside a living 

 organism like those which take place outside .f' In what respects are they different.'' 



3 How is the energy of protoplasm derived? 



4 What kinds of energy are released by protoplasm? 



5 In what respects is osmosis like the passing of water through a sieve? In 

 what respects is it different? 



6 What relation is there between temperature and the rate of diffusion? 



7 What conditions will produce turgidity in living tissues? 



8 In what ways do living things adjust themselves to changes in water sup- 

 ply? What conditions produce the most severe changes in water supply? 



95 



