22 



FIRST STUDIES IN PLANT LIFE 



the root-cell is stronger than the fluid in the earth, 

 and BO the earth-fluid passes into the root-cell. 



10. Why does too much salt in a soil hurt 

 plants ? Water the earth in a pot containing some 

 of your sunflower seedlings with a strong solution of 

 salt. The outside fluid is now the stronger ; and so 

 the fluid in the roots will pass out into the earth, and 

 the seedlings will wilt. This will help you to see 

 why most plants cannot grow in soils that contain 

 much salt. At Mildura whole orchards have been 

 ruined by soil containing too much salt. In good 

 soils the fluid in the root-cells is always stronger than 

 the earth-fluid ; and so there is nothing to check the 

 flow into the roots. An easy experiment will make 

 all this clearer. 



11. A mal<e-believe plant-cell. Fill a small 

 wide-mouthed bottle quite full with 

 water in which some sugar has been 

 melted. From a clean sheep's 

 bladder cut out a cover for the 

 mouth. Tie this firmly, and place 

 the whole bottle on its side in a 

 vessel of water. In a day or two 

 take it out, and note how the bladder- 

 lid has bulged out. The strong fluid 

 inside the bottle has sucked in some 

 of the weaker fluid. Place now the 

 bottle in a vessel containing a very 



strong sugar-fluid ; using more sugar than will melt. 

 This causes fluid to pass from the sugar-fluid inside 

 to the stronger sugar-fluid outside, and the bladder- 

 Ud no longer bulges. Now, if instead of a bottle with 

 a bladder-lid, we could try a root-cell, we should see 



in imitation plant- 

 cell, after being 

 ImmerBed in water. 



