220 TRANSPIRATION. 



280. Boot Absorption : Corrosive Action of Boots. 



It is readily shown that roots are able to bring into solu- 

 tion substances which are insoluble in pure water, that 

 roots have an acid reaction, and that they at any rate give 

 out carbon dioxide which dissolves in water to form 

 carbonic acid. 



(1) Half fill a small flower-pot with wet sand or fine 

 soil, insert a flat slab of marble with the upper surface 

 polished ; fill up the pot with sand, and plant a soaked 

 Bean or other seed so that when the roots reach the 

 marble they will grow over it horizontally. After about 

 ten days, remove the marble, rinse it with water, and note 

 the lines of corrosion where the root and its branches have 

 removed the polish from the surface. 



(2) Grow seedlings with their roots resting on blue lit- 

 mus paper wetted with distilled water, and note the change 

 in colour where the roots touch the paper. Another plan 

 is to use gelatine solution (1 part sheet gelatine to 5 parts 

 water) coloured with litmus solution made blue with lime- 

 water. Place some of this gelatine in a saucer, set in it 

 some germinated Peas or Beans with radicle 3 to 6 cm. 

 long, and note the change in colour (blue to red) of the 

 gelatine around the roots. Or place the gelatine in the 

 tube of a funnel stoppered with a small cork, support 

 the funnel, insert a Pea seedling with its roots in the gela- 

 tine, add cotton soaked in distilled water to keep the seed 

 moist and cover the funnel with a glass sheet, 



(3) To show that roots give out carbon dioxide, which 

 on being dissolved in water yields acid, grow seedlings for 

 a short time with their roots dipping into lime-water ; set 

 up a control experiment with a jar containing lime-water 

 but no plant. 



281. Boot Absorption: de Saussure's Law. The roots of a 

 plant placed in solutions of salts do not necessarily absorb the water 

 and the salt in the same proportion. This is called de Saussure's 

 Law, though he only observed the special case in which the root was 

 placed in a relatively strong solution and absorbed less than the due 

 proportion of the salt and more than that of the water. 



(1) Place any rooted plant e.g. a Maize seedling raised in culture 

 solution for a day in distilled water, and then transfer it to a jar 



