8 Carbon Assimilation. 



phyll. Herlitzka (1912) has shown that the spectrum of living leaves 

 agrees with that of colloidal chlorophyll solutions while both differ 

 in the same way from the spectrum of true chlorophyll solutions. 

 Willstatter's own experiments confirm the observations of 

 Herlitzka. He made measurements of the bands in the spectrum 

 of leaves of different plants and found them to occupy the same 

 positions as the absorption bands of the spectrum of colloidal solutions 

 of pure chlorophyll a. 



Again the condition of the chlorophyll in fresh leaves is altered 

 if the leaves are plunged in boiling water. After such treatment 

 the chlorophyll is much more easily extracted. Microscopic 

 examination shows that the chloroplasts are deformed as a result of 

 such treatment, they are displaced from the normal position in the 

 cell and diffusion out from them of chlorophyll follows almost 

 immediately. Externally the leaves change in colour to a deep 

 green. Spectroscopically this change in colour is shown to be 

 accompanied by a displacement of the absorption bands towards 

 the violet end of the spectrum so that they occupy practically the 

 same position as those in the spectrum of a chlorophyll extract. 

 This is explained at once on the view that the chlorophyll has 

 changed from a colloidal to a true solution and is now dissolved in 

 waxy substances which have become liquid as a result of the 

 alteration of temperature. As would be expected, pure acetone and 

 ether easily extract the pigment from a powder made from leaves 

 previously steeped in boiling water. 



It is worth mentioning that if fresh nettle leaves are treated 

 with acetone or other solvents, and are then examined spectroscopi- 

 cally when they have become deep green but before any pigment 

 Jias diffused out of the tissues, the same bands in the spectrum are 

 observed as with the spectrum of the extract. It is thus possible to 

 obtain within the leaf tissue a solution of the same kind as that 

 obtained by extraction. 



The various chlorophyll samples obtained by Willstatter by 

 different methods of extraction are identical, whether obtained from 

 fresh leaves, or from leaves put in boiling water, or frojn dried leaves. 

 They showed no difference in chemical composition, solubility oi- 

 optical properties. 



While in the higher land plants examined the same fourpigment 

 are always present, and the ratio of the quantities in which the four 

 are present does not vary very much, Willstatter found a somewhat 

 marked variation in the green algas, and a very different state of 

 affairs in the brown algae. 



The green alga examined was ULva lactuca. Here were found 



