THE CHLOROPLAST PIGMENTS 



465 



CHLOROPHYLL 



A review of our knowledge concerning 

 chlorophyll will now be given to show 

 what the various workers have discovered 

 regarding this pigment, which is so promi- 

 nent in the plant kingdom. Maybe by 

 reassembling our knowledge a new view 

 may be gained which may prove of value 

 to those who are not directly interested in 

 the green pigments. The history of our 

 ideas concerning the chloroplasts will 

 first be reviewed. 



THE CHLOROPLASTS 



Comparetti was perhaps the first person 

 to mention the green granules which we 

 now call chloroplasts. Apparently he 

 saw also the grains of starch which are 

 enveloped by the green material, though 

 he never guessed what they actually were. 

 Sprengel, Treviranus and later Turpin 

 believed that these green granules were 

 really vesicles which gave birth to new 

 cells. Moldenhauer believed that the 

 grains of chlorophyll were derived from 

 the coagulation of the green sap of the 

 cells. Later Treviranus stated that the 

 structure of the chloroplast consists of an 

 albuminous globule with which the green 

 material is mixed. Dutrochet considered 

 the small green grains in the cells at the 

 base of the petiole as equivalent to the 

 nerve corpuscles in animals. 



Mulder thought that a grain of chloro- 

 phyll could bring about the metamor- 

 phosis of a grain of starch with the sole 

 help of the nitrogen material dissolved in 

 the cell. Von Mohl recognized that 

 chlorophyll occurs sometimes in irregular 

 masses and sometimes in definitely formed 

 grains, which may show one or more 

 starch grains surrounded by a green jelly. 

 Nageli opposed the view of von Mohl that 

 the chlorophyll grains are composed of a 

 nucleus of one or more starch grains, sur- 



rounded by a layer of chlorophyll. Nageli 

 held that the chlorophyll grain is a vesicle 

 and should be classed with the other 

 colored globules in the cell sap. These 

 green and colorless vesicles he assumed 

 were analogous to cells and held that the 

 cell is built up of these vesicles just as an 

 organism is built of cells. Nageli later 

 modified his views and considered chloro- 

 phyll grains as vesicles with the green 

 color restricted to the surface and each 

 one bound by a cellulose membrane. He 

 considered them to be composed of a 

 protein substance whose surface is covered 

 by a condensation membrane formed by 

 contact of the grain itself with the cell 

 sap. Von Mohl altered his original con- 

 ception and recognized that although 

 starch and chlorophyll are often found 

 together they nevertheless arise independ- 

 ently. 



Sachs found that chlorophyll is always 

 united to definite portions of the proto- 

 plast. The amount of pigment is rela- 

 tively very small, for its removal affects 

 neither the shape nor the volume of the 

 ground substance, which is always a solid, 

 soft body containing extremely small 

 vacuoles in which the chlorophyll is 

 generally uniformly distributed. The 

 chloroplasts are always imbedded in the 

 cytoplasm and are never in contact with 

 the vacuole or the cell wall. With few 

 exceptions starch grains arise in the homo- 

 geneous solid substance of the chloro- 

 plasts. Sometimes drops of oil form in 

 the chloroplast. Hofmeister developed 

 his views further and held that the 

 chlorophyll grain is composed of two 

 layers, the peripheral layer being denser 

 than the inner one. 



Briosi was the first to recognize oil 

 droplets in the chloroplasts of a patho- 

 logical condition. In some plants oil 

 forms instead of starch, and the oil 

 exists in finely divided particles between 





