x THE PHYSIOLOGY OF NUTRITION 123 



exception of where it had been exposed to light, is pale in 

 colour. This shows that light is necessary for the formation of 

 starch. 



Only Green Plants can Assimilate. Those plants 

 which are destitute of chlorophyll must obtain their carbonaceous 

 food in some other form. The Dodder and the Broom-rape 

 obtain their carbon from the host plant (p. 24) upon which 

 they live, hence they are said to be parasites. Some plants 

 obtain the carbon which they require from decomposing 

 vegetable matter ; they are called saprophytes. The Bird's 

 Nest Orchid is a good example. 



EXPT. no. Place a little lime water in a saucer, and leave it on a 

 table for an hour or two. 



(i) The surface of the lime water will turn milky. 



(ii) This shows that carbon dioxide exists in the air. 



EXPT. in. Prepare some carbon dioxide by acting on marble with 

 hydrochloric acid. Fit up the apparatus shown in Fig. 145. Place a 

 few pieces of marble or limestone in 

 the flask and cover with water ; pour 

 strong hydrochloric acid down the 

 funnel till the action is brisk. Col- 

 lect a bottle of the gas. This can 

 be done by placing a delivery tube 

 into the bottle. When the contents 

 put out a light held just below the 

 outside of the mouth of the bottle, it 

 is full of carbon dioxide. Turn the 

 bottle wrong side up, and place it 

 over a branch with leaves which is 

 placed in a glass of water. Expose 

 to light for a few hours, and then 

 test with a light. The light will 

 burn. This shows that the leaf has FlG - MS- -Diagram of apparatus for the 



, i- -j i preparation of carbon dioxide. 



taken in carbon dioxide and given 



out oxygen. 



EXPT. 112. Place a green plant under an orange or red coloured 

 bottle. Expose to a bright light for a few days. Examine a leaf of 

 the plant in the following way : 



(i) Dip the leaf in boiling water. 



(ii) Bleach in methylated spirits till white. 



(iii) Place in cold water to displace some of the spirits. 



(iv) Cover with iodine solution. Note 



(v) The leaf will be coloured blue black. This shows that green 

 plants use the rays of light from the red end of the spectrum. 



If a red bottle cannot be procured, the experiment can be performed 

 by building around the plant panes of red glass. 



