THE ASSIMILATION OF CARBON BY AUTOTROPHIC PLANTS. I 109 



progress has been made in the chemical investigation of true chlorophyll during 

 the past few years, and research has shown that it is an exceedingly comphcated 

 body, in the composition of which lecithins and, perhaps, also proteid com- 

 pounds take part. A detailed exposition of the chemistry of chlorophyll, from 

 the pen of Marchlewski, will be found in Roscoe and Schorlemmer's Lehr- 

 buch d. Chemie, vol. VIII, 1901. Czapek (1902) also gives a summary of the 

 chemistry of chlorophyll ; in both works, and especially in that of March- 

 lewski, a full list of the literature is given. 



There is, further, a series of by-products of chlorophyll known to us, of 

 which we may mention one only, viz. phylloporphyrin. This substance, occur- 

 ring in the form of dark red-violet crystals, has a great likeness to a by- 

 product of the colouring matter of the blood, haematoporphyrin. This likeness 

 is demonstrated by comparison of the absorption-spectra of the two bodies. 

 These spectra are identical save in one respect, viz. that the absorption bands 

 of haematoporphyrin are displaced somewhat towards the red end (Fig. 25). 

 A likeness is also apparent in the chemical composition of the substances, for 

 haematoporphyrin has a composition represented by the formula CigHigNjOj, 

 while that of phylloporphyrin is represented by C1SH18N2O. Both substances. 



7 



JT" 



Fig. 25 Absorption spectra, / of phylloporphyrin (in ether) ; //, of haematoporphyrin (in ether). After 

 Marchlewski, in Roscoe and Schorlemmer's Lehrbuch der Chemie, vol. VIII. iqoi. 



on dry distillation, yield pyrrol. In spite of this agreement in chemical and 

 physical characters, chlorophyll and the colouring matter of the blood have 

 quite distinct physiological duties to perform. 



After this digression on the characteristics of chlorophyll we may return 

 to the consideration of the problem as to whether the dye alone, or only when 

 in combination with the living protoplasmic basis of the chloroplast, is con- 

 cerned in carbon-dioxide assimilation. 



As a matter of fact the assertion has frequently been made that a solution 

 of chlorophyll may, apart from the living substratum, be capable of abstracting 

 oxygen from carbon-dioxide. Kny (1897) has, however, given most convincing 

 proof that this is not so ; for when he investigated oil-drops containing chloro- 

 phyll by the bacterium method, not a trace of oxygen was to be found. 

 Czapek (1902) has carried this investigation a step further. He introduced 

 chlorophylliferous oil-drops into colourless protoplasm, but was unable to find 

 any evidence of the excretion of oxygen in the case of cells thus artificially 

 provided with the dye. It would appear, therefore, that the plasmatic 

 basis is quite as essential for the performance of the function carried out by the 

 chlorophyll -apparatus as the dye, and that other selected parts of the cyto- 

 plasm cannot assume the duties of the plasma of the chloroplast. 



Many facts, ascertained recently, of which we shall speak later on (Lecture 

 XVII), render it not improbable that certain chemical compounds, perhaps quite 

 independently of the hving chloroplast, assist in the carrying out of the ' chloro- 

 phyll function '. The experiments of Friedel (1901) and Macchiati (1903), 

 aiming at the isolation of these bodies, have not, however, been successful 



