THE ASSIMILATION OF CARBON BY AUTOTROPHIC PLANTS. I 107 



chlorophyll are capable of assimilating carbon-dioxide. [Molisch (I.e.) finds 

 that etiolated chloroplasts are quite inactive ] 



That it is not the entire chlorophyllaceous cell, but only the chloroplast 

 in particular that is the agen^ in the decomposition of carbon-dioxide, may be 

 proved by the following observations : — If one allows two small circles of light 

 to fall on a Spirogyra cell (with an open chlorophyll band) surrounded by 

 bacteria, so that one plays on the chloroplast and the other on the colourless 

 cytoplasm, it will be seen that an active assembling of bacteria occurs only in 

 the first field of light (Fig. 23, ///). Again, it has often been observed that 

 solitary chloroplasts isolated from cells are able for a long time to assimilate 

 whilst colourless cytoplasm is quite incapable of doing so. [Molisch's (1904, 

 Bot. Ztg. 62, I, i) results should be compared in this relation. He was able to 

 show, with the aid of luminous bacteria, that assimilation of carbon-dioxide could 

 be carried on by individual chloroplasts taken from dried dead cells.] The 

 disputed question (compare Kny, 1897, 1898; Ewart, 1898) as to whether such 

 functional chloroplasts must be still surrounded by a layer of protoplasm or 

 not, is of less interest in this relation ; it is, however, clear that in the long 



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• ' / i*-- 



'. ,1, , >■ - ' • • ■ •' 



!• . ?. '. , . • I '_* ," ■ ' ■ 



•" ji 





.■•': 



J 



I '. 





• • • •/;. ' 



Fig. 23. /, a spherical, green alga centrally placed, and uniformly surrounded by bacteria (in darkness). 

 X 150; //, the same preparation after a brief illumination ; ///, cell o^ Spirogyra illuminated at two places; the 

 bacteria collect only where the beam of light touches the chloroplast. x 350. (After Engelmann, 1894.) 



run it is only a chloroplast enclosed in protoplasm that can assimilate, and there- 

 fore it is not of so much importance to know how quickly it loses its capacity 

 when isolated from the plasma. The dependence of the chloroplast on the 

 protoplasm need not be directly connected with the process of assimilation. 



Now that we have shown that it is only the chloroplast that assimilates 

 in the cell, and that too only when it is green, we have next to attempt to settle 

 the question as \o 'whether it is the pigment itself, the chlorophyll, that is the 

 agent in the decomposition of carbon-dioxide, or whether it can carry out its 

 function in the absence of the protoplasmic basis. 



This problem compels us to examine more closely into the physical and 

 chemical characters of the chlorophyll. [The recent literature on the subject 

 of chlorophyll is to be found in Czapek, I.] 



In certain chloroplasts green granules or drops are visible, distinct from 

 the colourless ground substance, and the green colour can be extracted by 

 means of alcohol. This crude alcoholic solution of chlorophyll is characterized 

 from a physical point of view by its fluorescence and by its absorption spectrum. 

 By transmitted light the solution is a beautiful green, but deep red by reflected 

 light, but this fluorescence appears only in the solution and never in the chloro- 

 plasts, and we should naturally conclude from this that the dye occurs in the 

 chloroplast in a state of combination (Reinke, 1883). The spectrum of crude 

 chlorophyll is shown at the top of Fig. 24. 



