THE FOOD OF PLANTS. 27 



8. The Decomposition of Chlorophyll. 



We place vigorous pot plants of Tropaeolum majus in the 

 dark, e.g., in a cupboard. If the temperature is not too low, the 

 leaves will already have experienced striking colour changes at 

 the end of eight days. The older leaves, although still juicy, look 

 yellow, while the younger are spotted, and the youngest are still 

 quite green. The absence of light, as is shown by microscopical 

 investigation of thin sections from the mesophyll of the Trop 1 *- 

 olum leaves, has had an important influence on the chlorophyll 

 grains. They have lost in size, and in place of the green pig- 

 ment only a yellow one is now present. 1 If filaments of Spiroryra 

 are for a long time (in my experiments for five or eight days, 

 temperature 15-20C) exposed in a glass containing some water 

 to continuous darkness, the chlorophyll bodies undergo considerable 

 changes. In many cells certainly green spiral bands are still 

 present, in others, however, a breaking up of the chlorophyll 

 bodies into irregular balls has already set in, the disorganisation 

 being associated with a change in the colour of the pigment. 



The chlorophyll in the cells also undergoes profound decomposi- 

 tions when brought in contact with acids. We lay filaments of 

 Spirogyra or Zygnema (I used the latter with special success) in 

 a mixture of 1 part of concentrated Hydrochloric acid,, and 4 parts 

 of water. The chlorophyll changes colour, and after some time 

 (sometimes not for twenty hours) there appear in the chlorophyll 

 bodies, especially at their edges, brownish or rust-coloured masses, 

 decomposition products, due to the action of the Hydrochloric 

 acid (Hypochlorin reaction).- 



A crude chlorophyll solution (prepared by treating green plant 

 structures with alcohol) similarly undergoes essential changes 

 when treated with acids. If, e.g., we treat such a solution with 

 very dilute Nitric or Hydrochloric acid, its beautiful green colour 

 is at once lost, and it assumes a brownish hue. 



The crude alcoholic solution of chlorophyll of course contains, 

 besides chlorophyll itself, a whole series of other substances, but 

 we may nevertheless conveniently make use of it to prove that 

 chlorophyll is highly sensitive to light. In the dark an alcoholic 

 solution of chlorophyll remains unchanged for a long time ; it 

 only very gradually changes in colour. Diffuse light does not act 

 very rapidly on a crude chlorophyll solution, but direct sunlight 

 does ; in direct sunlight such a solution very distinctly changes 



