NUTRITION 57 



numbers and in numbers about equal in all the colors, 

 though somewhat more in the green-blue. 



That both living protoplasm and chlorophyll pigment are 

 necessary is shown, on the one hand, by the ineffectiveness 

 of plastids well developed but colorless, and, on the other, 

 by the complete inability of chlorophyll solutions either 

 themselves to liberate oxygen from carbon-dioxide in the 

 light or to enable colorless plastids to do so. The energy' 

 needed must be absorbed by chlorophyll in direct contact 

 with and enclosed in living protoplasm, otherwise both 

 energy and chlorophyll are useless. Chlorophyll grains 

 mechanically isolated from living cells continue for a time to 

 absorb carbon-dioxide and to give off oxygen, as may be 

 shown by motile aerobic bacteria.* But if such isolated 

 plastids are so treated that they pass over into a state of 

 anaesthesia, they no longer absorb carbon-dioxide, and 

 liberate oxygen although they still absorb light rays. The 

 living protoplasmic body of the plastids, together with the 

 chlorophyll pigment contained in it, are the organs by 

 which plants begin the manufacture and elaboration of their 

 food. These organs are to a high degree independent of the 

 other organs of the cell and of the cytoplasm itself, but not 

 entirely so ; they are still cell-organs. 



For the formation of chlorophyll in cells which normally 

 contain it two conditions may be mentioned as of special 

 importance, namely, illumination and the presence of iron. 

 Most plants fail to produce chlorophj'll in darkness, al- 

 though a larger number than was formerly supposed are 

 now known to produce it regardless of the illumination. 

 Among these may be mentioned the seedlings of conifers 

 and maples. The influence of light on its formation in most 

 plants must be regarded as a stimulus rather than a pre- 

 requisite, although the work of the chlorophyll pigment can 

 be done only in the light. Then only is there energy to be 

 absorbed, and the radiant energy, falling upon the cell, will 

 stimulate it to develop a more effective absorbent than wall 

 and cytoplasm afford. The action of iron also, since it is in 



* Ewart, A. J. Can isolated chloroplastlds continue to assimilate? 

 Bot. Centralblatt. Bd. 75. No. 2. 1898, and other papers there cited. 



