STOMATA AND DARKNESS. 115 



DARKNESS. 



Concerning the relation of prolonged darkness to the physiological activity 

 of stomata we have some data, but the effect of this condition upon the con- 

 tents of the guard-cells has received scant attention. Francis Darwin (1898), 

 by means of the horn hygroscope, came to the conclusion that "there is a 

 tendency to a gradual opening of the stomata in continued darkness, " though 

 with the "same irregularity" that he had "noted in regard to nocturnal 

 closure." 



Sachs (1862, p. 369; Beilage, 1863, p. 4), pointed out that starch occurs 

 in the guard-cells of etiolated plants, and that stomata develop completely 

 in entire darkness. Similarly, Leitgeb (1888) found that, in the etiolated 

 petioles of Crambe cordifolia, in the complete absence of chlorophyll, and 

 entirely without the influence of light, the stomata were wide open, and that 

 the guard-cells were filled with starch. MacDougal (1903), also, noted that 

 the stomata in many plants which had been grown in total darkness were 

 open. It seems clear from previous studies that stomata may perform move- 

 ments, at least the opening movement, and that starch may accumulate 

 in the guard-cells, in the entire absence of light. 



As in the case of the other experiments to determine the effect of the sev- 

 eral factors upon the changes in the character of the contents of the guard- 

 cells, I have taken advantage of the presence and absence of starch in the early 

 and late hours of the morning, respectively, to begin experiments at these 

 times, thus enabling me to determine if the amount of starch and of oil will 

 decrease in the dark, and also if it will increase, and what is the behavior 

 of the stomata as to movement. 



VERBENA. 

 Experiment 208. Cutting placed in dark at n a. m., March 28, till 3 p. m., March 29. 



A moderate amount of starch in the chlorenchyma, but none in the stomata 

 at the beginning of the experiment. At the close of 28 hours' exposure to 

 darkness, a medium amount of starch is found in the guard-cells, but no trace 

 in the chlorenchyma. Stomata closed, but as the leaves were slightly wilted 

 no conclusion may be drawn. 



Experiment 144. July 4, 1905. In darkness from 8 a. m. on. 



July 4, 8 a. m. Cutting placed in the dark, 2.8 to 8.4; 5.5 to 8.4 micra. 



ii a. m. Little or no starch in guard-cells; 2 to 3 micra. 



i p. m. Starch in the guard -cells; 2 to 3 micra. 



3 h i5 m p. m. Starch plentiful in the guard-cells, but none in the palisade tissue. 



7 p. m. Starch plentiful in the guard-cells, but none in the palisade tissue. 



July 5, 8 a. m. Stomata contain plenty of starch and are 2 to 5.5 micra open. 



NOTE. Apparently a slight opening at the close of 24 hours. 



