CHLOROPHYLL AXD THE CHLOROPLASTS 381 



tein as well as lipoid substances. There has been considerable discus- 

 sion as to whether the chloroplasts possess a membrane and opinions are 

 still at variance regarding this point.^^ 



There is a phase boundary at the surface of the chloroplast between 

 this and the surrounding cytoplasm. Senn ^^ is of the opinion that the 

 chloroplast is bounded by a peripheral layer, the peristromium, while 

 Meyer ^* is of the opinion that the latter is a part of the cytoplasm. 



The manner in which the pigments are distributed or held in the 

 chloroplasts is not clearly understood. According to Meyer's views the 

 pigments are dissolved in the oil of the grana which are imbedded in 

 the colorless stroma. It has also been stated that the pigments are 

 uniformly distributed through the chloroplast while some investigators 

 have concluded that the chlorophyll is on the surface of the chloroplasts.*^ 



Of considerable interest is the fact that chloroplasts have been removed 

 from the cells in which they were contained, and it has been found that 

 thus isolated, the chloroplasts continue their photosynthetic activity for 

 some time.^*^ While Kny ^' has maintained that in these preparations 

 some cytoplasm was still adhering to the chloroplasts, which made pos- 

 sible their activity, there is no doubt that the method ofifers a splendid 

 means of studying their behavior. With modern cytological technique it 

 is possible that much valuable information could be gained by the develop- 

 ment of this method. 



Finally, another property of the chloroplasts which may exert an in- 

 fluence on the rate of photosynthesis should be mentioned. It has been 

 observed that the chloroplasts orient themselves in the cell in response 

 to the intensity of light. Owing to differences in the number of chloro- 

 plasts in a single cell and other physiological and morphological prop- 

 erties, the form which this orientation takes varies in different species. 

 These phototactic reactions of the chloroplasts have been extensively 

 studied and the results have been recorded diagrammatically. We shall 

 here only indicate the principle of this orientation. Thus, for example, 

 in light of moderate intensity, the disk-shai>ed chloroplasts may be so 

 arranged within the cell that their flat surface is at right angles to the 

 incident radiation. In this manner maximum absorption of the light is 

 attained. When the illumination intensity is high, the ix)sition of the 

 chloroplasts is changed ; under these conditions the edge of the disk is in 

 line with the incident rays. Many variations of this orientation of the 

 chloroplasts resulting from alterations in the intensity of light have been 



•"Zacharias, Bot. Zeitg., 41, 209 (1883). Schmitz, "Die Chromatophoren der 

 Algen," Bonn, 1882. . . 



" Senn, "Die Gestalts- und Lageveranderungen der Chromatophoren," Leipzig, 

 1908. 



"Meyer, Ber. bot. Gcs.. 40, 161 (1922). 



'^ Priestley and Irving, Ann. Bot., 21, 407 (1907). 



^Englemann, Bot. Zcitg.. 39, 446 (1881). Ewart, .luur. Linncan Soc, 31, 364 

 (1896) ; Bot. Ccniralb., 72, 289 (1897) ; 75, 2,2, (1898). 



"Knv, Ber. bot. Ges., 15, 388 (1897): Bot. Ccntralb.. 73, 426 (1898). Kos- 

 tytschew, Ber. bot. Ges., 39, 333 (1921). 



