THE QUARTERLY REVIEW OF BIOLOGY 



some of the earlier workers thought that 

 it was starch. However, the staining 

 properties of the ground substance indi- 

 cate that it is a protein. In general, the 

 reaction of chloroplasts to the histological 

 stains shows that they contain protein. 

 Also, the proteolytic enzymes, pepsin and 

 bromolin, will digest the chloroplasts. 

 The evidence shows that there is no doubt 

 as to the real nature of the ground sub- 

 stance of which the chloroplast is com- 

 posed. There also appears to be no 

 argument as to whether there is or is not a 

 true ground substance. However, there 

 is an argument concerning the physical 

 state of the ground substance. 



Zirkle says that the physical state of the 

 ground substance is a gel rather than a sol, 

 which can be demonstrated by tearing 

 apart the chromatophores . Besides it is 

 hard to conceive of a sol maintaining a 

 definite structure such as the ground sub- 

 stance possesses in the living cell. Since 

 there has been so little investigation on 

 this subject it cannot be said that the 

 matter is definitely settled yet. Some- 

 thing has already been said regarding the 

 location of the pigments in the chloro- 

 plasts but a summary of our ideas on this 

 subject will be beneficial at this time. 



The opinion is generally, though not 

 unanimously, held that the chloroplast 

 pigments are more or less restricted to the 

 peripheral region. Investigators who 

 have noticed the granular appearance of 

 the chromatophores are almost equally 

 divided as to whether the important pig- 

 ments are located in the granules them- 

 selves or in the ground substance in which 

 the granules are imbedded. Lloyd ob- 

 served that it is the non-granular part of 

 the stroma which emits fluorescent light. 

 Sachs believed that both granules and 

 ground substance are colored, while 

 Chodat thought that the lacunae within 

 the chromatophores are lined by a thin 



pigment layer. Zirkle found by examin- 

 ing the chloroplasts in light of various 

 wave lengths, corresponding to the absorp- 

 tion band of each of the different pigments, 

 that the pigments are intimately mixed 

 and evenly distributed throughout the 

 ground substance. The only parts of the 

 chloroplasts not colored were the pores 

 and the starch inclusions. 



The state of chlorophyll in the chloro- 

 plast has been investigated by many 

 workers . Reinke investigated the proper- 

 ties of the pigment chlorophyll both with- 

 in the living plastid and in solution. He 

 found a slight fluorescence in the living, 

 green plastid and assumed that there must 

 be some sort of combination between 

 pigment and plastid and that the pigment 

 existed not as a solution but as finely 

 divided particles. 



Herlitzka in investigating the absorp- 

 tion spectra of chlorophyll concluded that 

 it is held in a solution of different form 

 from that of its usual solutions with 

 organic solvents; this form being that of a 

 colloidal solution. Iwanowski came to 

 the conclusion that chlorophyll must 

 exist in a colloidal form in the living 

 chloroplast, for it is in the latter state that 

 it is most indestructible. 



Stern seems to possess a slightly different 

 view from most investigators, for he 

 observed that chloroplasts fluoresce some- 

 what, and this led him to the view that 

 chlorophyll is present in the cell in a true 

 lipoid solution. 



Lloyd brings forth evidence to show 

 that chlorophyll does not exist in solution 

 in the chloroplast but that it is present in 

 some other form. Later in the same year 

 he found that chloroplasts of leaves and of 

 green algae show a deep red fluorescence to 

 a marked degree. He finds that the part 

 of the chloroplast which emits fluorescent 

 light is the non-granular stroma. 



Arnaud assumed that chlorophyll is held 



