112 THE PHYSIOLOGY OF STOMATA. 



When begun at the time of starch minimum, as the day advances — 

 (i) Starch is increased in amount in the guard-cells. 



(2) Oil is reduced in amount. 



(3) The starch content of the chlorenchyma continues to increase. 



(4) The stomata gradually close. 



The conclusion to be drawn is, therefore, that the course of events is nor- 

 mal as regards both the guard-cells and chlorenchyma and as regards the 

 movements of the stomata. Such quantitative differences as were observed 

 may be referred to the reduced amount of illumination available under the 

 conditions of the experiments. Differences of this kind become more marked 

 when the experimental conditions are long sustained, as in experiment 220 

 displayed above. As there shown, the starch in the guard-cells and chloren- 

 chyma appears to become somewhat depleted, and this is referable to a slight 

 general starvation. The same thing, but more pronounced, has been shown 

 to occur in the corresponding experiment with the blue light, for which see 

 beyond (fig. 39). 



BLUE LIGHT.* 



Experiment 217. — Verbena ciliata, April 25. 



Set up at 6 h 30 m p. m., April 24, bell-jar remaining upon the same twigs as were used in 

 experiment 215, beyond; night minimum temperature, 50 F. 



6 h 30 m p. m., April 24, control: Starch in guard-cells approaching its maximum; no 

 oil; starch in chlorenchyma plentiful; o to 2 micra. 



4^30™ a. m. April 25, control: Starch abundant in guard-cells, but no oil; minute gran- 

 ules of starch in chlorenchyma (chloral-iodine) ; o to 3 micra. 



io h 30 m a. m., control: Oil drops; starch plentiful in chlorenchyma; starch depleted but 

 not absent from guard-cells; 2 to 4 micra. 



nh^Qtn a m ; control: Oil drops very large; 4 to 8 micra; starch content of guard-cells 

 low, presumably at minimum. 



Experimental part: 2 to 8 micra; no oil; bell-jar maximum temperature, 90 F. ; air 

 temperature, 95 F. (plate 11, fig. 6). 



The starch in the guard-cells is entirely absent from certain stomata which 

 are wide open and their plastids small. Some stomata, however, have rather 

 large plastids and appear lakey, while a few are deeply-staining. An average 

 stoma, as regards starch, appears as at the same hour on the 24th (experi- 

 ment 2i2 ; plate 9, fig. 2). The amount of starch appears to be correlated with 

 the degree of opening. No starch in chlorenchyma. 



A particular stoma with a very wide opening (8 micra) was noted; the 

 plastids were very small and but little starch was present, in minute granules. 



* Between 0.48 and 0.42. 



