THE CHLOROPLAST 105 



macromolecule (on the assumption that the macromolecule is 65 A in 

 diameter ) . Therefore, the chlorophyll-protein complex would have a 

 molecular weight of the order of 68,000. It must be remembered, 

 though, that chlorophyll could be complexed with different proteins 

 in the various plant species, and that the molecular weights would 

 vary, depending upon the kind of protein. The nature of the pro- 

 tein, or how chlorophyll is complexed to the macromolecule, has 

 not yet been elucidated. 



TABLE 4 

 Analysis of Euglena Chloroplastin 



w dry wt, mg/m! 27.3 



n mg nitrogen/ml 0.36 



/; moles chlorophyll 1 6.3 X 10"^ 



p' moles chlorophyll/1 calculated from w/M' 9.4 X 10"^ 



M mol wt calculated from M' 38,000 



M mol wt calculated from w, n, and p 30,000-60,000 



Crystallization and Periodicity 



The next steps in our exploration were to see if there were any 

 possible wav of accounting for such a lamellar structure for the pig- 

 ment complex in the chloroplast. Here I would like to refer to some 

 experiments on the Liesegang phenomena (Hedges, 1932). Liese- 

 gang observed the formation of periodic structures in the course of 

 staining histological specimens by the Golgi technique (i.e., the 

 impregnation of tissue with potassium dichromate and silver ni- 

 trate ) . The Liesegang phenomenon has been often cited as a model 

 for study of growth and differentiation in living cells. Antigen-anti- 

 body reactions in gels also have been compared to Liesegang ring 

 phenomena. 



The formation of the rings can be observed if a drop of 15 per 

 cent silver nitrate is placed on a sheet of gelatin which has been 

 impregnated with about 0.4 per cent potassium dichromate. The 

 silver slowly diffuses into the gelatin, there reacts with the potassium 

 dichromate, and silver dichromate is precipitated in the gelatin. 

 The precipitation is not continuous but forms a series of concen- 

 tric rings separated by clear spaces in the gel. ( Fig. 8d. ) There are 

 many other such examples; if ferric chloride be added to gelatin 

 and a drop of potassium ferrocyanide solution placed in the center, 

 blue rings of ferriferrocyanide will be formed. Light can modify 



