LECTURE XIX. 



ORIGIN OF STARCH IN THE CHLOROPHYLL, AND IN THE STARCH- 

 FORMING CORPUSCLES: FURTHER BEHAVIOUR AND FATE 

 OF THE CHLOROPHYLL. 



It was stated at the end of the foregoing lecture that the starch arises in 

 the chlorophyll by means of the process of assimilation— i. e. by the decomposition 

 of carbon dioxide under the influence of light — and that it represents the first 

 product of assimilation hitherto known with certainty. The attempt may now be 

 made to establish these facts more definitely. 



If seedlings of the Gourd, Sunflower, Maize, or Garden-beans, or the sprouts 

 of Dahlias or Helianthus tuberosus are allowed to grow in the dark at a suf- 

 ficiently high temperature (i5°-'2 5°C), until development finally ceases, the tissues 

 of these etiolated shoots, as well as those of the roots, are at length entirely emptied of 

 assimilated substances. The plants in these cases consist almost solely of cell-walls, 

 protoplasm, and water. The most important fact, however, is that the small yellow 

 chlorophyll-corpuscles in the leaves contain no trace of starch, either in the chlo- 

 rophyll or in the other organs and tissues. If these plants, already green, or 

 even those taken immediately from the dark, be placed at a light window, 

 starch arises in the chlorophyll-corpuscles (which have previously become green) at 

 first in exceedingly small quantity, which rapidly increases in strong light. In the 

 course of several days, 6 — 20 according to the temperature, abundance of starch is 

 found in the chlorophyll, and subsequently also in certain layers of tissue in the 

 petioles and shoot-axes; this may be followed into the buds, the young leaves 

 of which now begin also to grow anew, since the starch produced in the chlo- 

 rophyll again supplies material from which the tissues of new organs may be 

 formed. By means of such investigations I first succeeded, in 1862, in experimentally 

 proving that the starch formed in the chlorophyll under the influence of light, 

 is the first visible product of assimilation \ In 1863 and 1864 I convinced myself^ 

 that the starch contained in the chlorophyll of normally developed leaves may 

 disappear again in long-continued darkness ; and that it is possible to bring about 



' Sachs, ' Uebcr den Einßuss des Lichtes auf die Bildung des Amylum in den Chlorophyll- 

 körnern^ Bot. Zeit. 1862, p. 365. 



^ Sachs, ' Ueber die Auflösung und Wiederbildung des Ain^luin in den Chlorophyllkörncrn bei 

 wechselnder BeleuchtuJig.' Bot, Zeit. 1864, pp. 289 and 322. 



