THE CHLOROPLAST PIGMENTS 



467 



special division of the two components, 

 chlorophyll and the ground substance, 

 could be observed, he was led to accept 

 the hypothesis that the lipoid and the 

 hydroid exist as fine emulsions. Meyer 

 concluded from his studies on Tropaeolum 

 majus that the "grana" are small oil 

 droplets always to be met with in the 

 growing chloroplasts. 



Stern on investigating the fluorescent 

 properties of chlorophyll came to the con- 

 clusion that as contained in the uninjured 

 cell it is in a true lipoid solution. Mange- 

 not considered oil as the first product of 

 the photosynthetic activity of the chloro- 

 phyll of Vaucheria. 



Chlorophyll is variously stated to be 

 dissolved in some oily substance which is 

 held in the channels and meshes of the 

 plastids or to exist in the form of a colloid. 

 From all of the evidence that can be 

 obtained it is evident that oil must exist 

 in all of the chloroplasts. This means 

 that chlorophyll and oil must exist 

 together in all green plants. However, 

 Zirkle says that when chloroplasts are 

 tested for oil the results are quite incon- 

 clusive. 



The nature of the boundary of the 

 chloroplast has been a subject concerning 

 which there has been much discussion. 

 Many investigators have observed that 

 when two chloroplasts come in contact 

 with each other the two green masses 

 remain intact and are separated by a 

 colorless zone. Tschirch cited this fact 

 to prove that a membrane exists surround- 

 ing the chromatophore. Chodat believed 

 that the appearance of this colorless zone 

 is due to the fact that the outer layer of 

 the ground substance is colorless, and 

 held that no membrane was present. 

 Meyer held that each chromatophore is 

 surrounded by a non-granular layer of 

 cytoplasm. Most of the earlier workers 

 believed that chromatophores were vesi- 



cles and Nageli at one time stated that 

 each chromatophore was surrounded by 

 a cellulose membrane. Later workers, as 

 von Mohl, Sachs and Meyer, do not admit 

 the presence of a membrane about the 

 chloroplast. 



Some more recent investigators have 

 denied and some have affirmed that a 

 membrane exists. Here by membrane is 

 meant a thin firm layer which is probably 

 conceived to be semipermeable. Zirkle in 

 a recent investigation recognized no such 

 structure. 



Today we recognize such things as 

 liquid membranes, and Zirkle sees no 

 reason why we cannot consider this inner 

 film of the cytoplasmic sheath as such a 

 membrane. The observed swelling of 

 chromatophores in pure water or in 

 aqueous solution of low osmotic value 

 does not seem to be due to any osmotic 

 property of this membrane, for that 

 portion of the chloroplast which swells 

 seems to be located within the ground 

 substance. Modern methods of investi- 

 gation also show us that a colorless zone 

 such as was noted by Tschirch and Chodat 

 can be readily demonstrated in the living 

 cells of Elodea. The thickness of this 

 zone varies from 1 to 0.15 micron and 

 seems to be correlated with the state of the 

 cytoplasm. When cyclosis is very slug- 

 gish the zone is thick; when the cell con- 

 tents are rapidly circulating the zone is 

 thin. No distinct zone could be observed 

 at all when the chloroplasts were rapidly 

 moving. Evidence shows that the chloro- 

 plast covering remains with it when it 

 circulates in the cell; yet this layer is not 

 constantly associated with the chloro- 

 plast, for its thickness is continually 

 changing. 



Workers have generally agreed that the 

 ground substance of the chromatophore is 

 a protein. It is true that Mulder con- 

 sidered it a wax derived from starch and 





