CH. Il] PHOTOGRAPHIC METHOD. 21 



(30) Gardiner's experiment^. 



A plant growing in a flower-pot (for convenience of 

 moving) is placed in the dark for 24 hours, or until the 

 leaves are found to be free from starch. One of the 

 leaves is now covered with a photographic negative and 

 left exposed to bright light out of doors, or in a greenhouse, 

 until the evening, when the leaf is tested for starch. It 

 will be found that an accurate copy of the photograph 

 has been printed in starch. 



(31) Effect of rays of different refrangihility. 



The effect of the different parts of the spectrum may 

 be demonstrated by a similar method as has been done 

 by Timiriazeff". In the absence of the necessary appa- 

 ratus we may compare the effects of light transmitted 

 through coloured fluids. Fill a couple of double-walled 

 bell-jars, (1) with potassium bichromate solution, (2) 

 with ammoniacal OuSO^ solution. Under each bell place 

 a young Tropseolum or Clover plant in a small pot, or a 

 seedling plant of any kind dug up and placed with its 

 roots in a bottle of water. The bell-jars should stand in 

 saucers of dry earth or sawdust, so as to ensure the 

 exclusion of colourless light. They must be exposed to 

 diffused light — in sunshine the temperatures are not the 

 same in the twx) bell-jars. The experiment may be 

 started in the afternoon and the leaves tested on the 

 following evening. 



' W. Gardiner, Annals of Botany, iv. p. 163. 

 2 Timiriazeft, Comptes rendus, T. ex. p. 1346. 



