166 



THE PLANT CELL. 



green part of a plant be placed in alcohol for some hours, the 

 chlorophyll is extracted, and, on adding benzine in equal volume 

 to this alcoholic extract, and shaking up the mixture, the benzene 

 separates the phyllocyanin and floats on the top of the alcohol, 

 the latter liquid retaining the phylloxanthin. 



By making an alcoholic extract of chlorophyll alkaline with 

 caustic potash, and examining the extract by means ot the 

 spectroscope (the tube or special vessel containing the chlorophyll 

 solution being placed in the path of rays of white light before 

 they reach the prism), some characteristic absorption bands may 

 be seen in the spectrum of white light which has passed through 

 the tube containing the chlorophyll. In all, seven such bands 

 occur in various parts of the spectrum, and they indicate that 

 chlorophyll absorbs certain of the rays of sunlight and allows 

 others to pass. The absorption bands are situated as follows 

 in the spectrum (see Fig. 112); — 



[I 



a 1 



2, C CL 



Fig. 112. — The Absokption Spectkl'm or CuLOROPHYLr, (see text). — 

 6, c, Fraunhofer lines in the red. d. The sodium band in the yellow 

 portion of the spectrum. 1, 2, 3, 4, 5, 6, and 7 are the bands in the 

 spectrum formed by the absorption of certain rays by the chlorophyll 

 (alcoholic slightly alkaline solution). 



One band (the I band) occurs in the red, between the Fraun- 

 hofer lines B and C, another in the orange whilst a third and 

 fourth are in the green portion of the spectrum. There are 

 also three broad bands in the blue and violet at the other 

 end (chemical rays). 



The significance of these bands is as follows; — Of the white 

 light which reaches a chloroplast, only those ra}s which are 

 indicated by the position of the absorption bands in the spec- 

 trum are made use of for the purposes of the assimilation of 

 COg and water, the other rays passing through. The chloroplast 

 is a specialised portion of the cytoplasm of a cell, and as such is 

 able to transform the energy derived 1)y the sifting out by 



