STOMATA AND DARKNESS. 119 



The conclusion reached was that the accumulation of oil does not take 

 place in the absence of light. The retention of starch and the inhibition of 

 opening in the absence of light is to be noted. 



Experiment 300. — Verbena ciliata, January n, 1907. 



11 a. m. Control showed no starch in the guard-cell, though a considerable amount in 

 the chlorenchyma. The guard-cell plastids were very small (plate 12, figs. 3, a, b, d, and 4). 



Jan. 12, 1 1 a. m., after darkness for 24 hours. Guard-cell plastids fully twice the diameter 

 and showing a distinct though not very pronounced general reaction. The black granules, 

 however, very distinct. Stomata 1 to 7 micra open; no starch in the chlorenchyma; no 

 starch in guard-cells of control (plate 12, fig. 5). 



The accumulation of starch at this time of the year is not as rapid as in 

 the warmer months. The same experiment was tried on December 27, 1906, 

 but the temperature was too low and the result of the trial was negative. 

 January 1 1 was unusually warm and the opportunity was used to repeat the 

 experiment, with the above result. 



SUMMARY FOR VERBENA. 



When the experimental conditions are imposed upon the plant in the early 

 morning, when the starch content is at its maximum and the oil at the mini- 

 mum, we find that during the following few hours, during which the starch 

 is normally reducing and the oil increases to a maximum — 



(1) The starch content of the guard-cells is not reduced. 



(2) The oil does not increase in quantity. 



(3) Starch is not formed in the chlorenchyma. 



(4) The stomata open little if at all. 



On the other hand, if the experiments are begun late in the morning, at a 

 time when the starch is absent and oil is present, and when a certain amount 

 of starch has already appeared in the chlorenchyma, we find that — 



(1) The starch is reformed more or less rapidly in the guard-cells. 



(2) The oil disappears. 



(3) The starch disappears from the chlorenchyma. 



(4) The stomata gradually close. 



During prolonged exposure for 3 days to darkness, starch continues to be 

 found, but no oil. After 6 days the general starvation of the leaf becomes 

 so pronounced that little or no starch may be found in the stomata. After 

 such extended subjection to darkness, upon being placed in the light starch 

 appears first in the chlorenchyma. The stomata do not, taken collectively, 

 become wide open, although, as Francis Darwin noticed, some opening does 

 take place. There is, however, considerable variation in the size of the 

 stomata. In one instance a maximum width of 10 micra (Verbena) was seen 

 after 7 hours of darkness. 



