EFFECT OF CHLOROPHYLL- AND STARCH-CONTENT 147 



Effect of the Chlorophyll- and Starch-Content 



of the Cell 



One of the internal factors in photosynthesis is the 

 presence of chlorophyll. The following investigation was 

 undertaken to correlate the number of chloroplasts with the 

 photosynthetic activity of the leaf. For this purpose three 

 different whorls of leaves were taken from the same Hydrilla 

 plant, one from the youngest portion of the stem 5 mm. from 

 the top, the second from the still young portion 2 cm. 

 below the top, and the third, a relatively old whorl, from 

 6 cm. lower down. Their photosynthetic activities were 

 measured by the number of bubbles of oxygen given out. 

 Microscopic examination of the leaves was also made to 

 determine the relative number of chloroplasts. Repre- 

 senting by 100 the activity of the youngest and immature 

 whorl (1) at the top, that of the second whorl (2) was 125, 

 while it was only 86 for the oldest whorl (3) of leaves lower 

 down. The activity was thus at its maximum in the 

 moderately young (2), and at its lowest in the old leaves (3). 

 The activity of the youngest leaves (1) exhibited a decline 

 under the continued action of light ; but it was uniform in 

 the leaves (2). Microscopic examination showed that the 

 youngest leaf (1) contained about 30,000 chloroplasts, while 

 the (2) leaf had as many as 60,000. The number of chloro- 

 plasts diminished to 25,000 in the oldest leaf (3). A relation 

 is thus found to exist between the number of chloroplasts 

 and the photosynthetic activity of the leaf. It should, 

 however, be borne in mind that the protoplasmic factor is 

 even more important, for it has been shown that excessive 

 stimulation induces an arrest or permanent abolition of 

 photosynthesis. 



Effect of excess of starch-content. — The Hydrilla plant 

 growing in the sun-exposed pond exhibits, as previously 

 stated, a relatively feeble photosynthesis. This may be 

 partly due to the after-effect of strong and continuous 



