STOMATA AND DARKNESS. I I 7 



subsequent 24 hours, the third day in the dark, the starch content increases 

 irregularly as regards different stomata. 



After placing in the dark the stomata close as normally and remain so. A 

 slight opening may occur between sunrise and 8 a. m. on the second day. 

 The starch content of the guard-cells is uneven at this time and the slight 

 opening of some stomata may be correlated with this condition. The starch 

 content of the chlorenchyma disappears once for all after a few hours. 



When stomata, taken at any time in the progress of the experiment, are 

 placed in water, they open to from 2.8 to 8.4 micra. 



When, after exposure to darkness for 24 and 48 hours, the plant is placed 

 in strong diffused light, the starch appears in the chlorenchyma more rapidly 

 than in the plastids of the guard-cells. Assuming that the guard-cell plastids 

 are capable of photosynthesis, this may mean that the products of this activ- 

 ity are used too rapidly to allow accumulation of starch, or on the contrary 

 assumption, that the stomata have to draw upon the chlorenchyma for the 

 materials which they use. There remains the possibility that both of these 

 conditions obtain in part. It remains clear that the stomata are less starved 

 than the chlorenchyma. 



Experiment 210. — Verbena, March 30, 1906. Cutting taken 5 h 30 m a. m. and placed in dark. 



5 h 3o m a. m. Normal; starch in abundance in the guard -cells; absent from the majority 

 of the chlorenchyma cells but found in some, due probably to a small amount of photo- 

 synthesis. (See also experiment 209.) 



n h 30 rn a.m. Experimental, o to 5 micra; starch abundant in the guard-cells; none 

 in chlorenchyma (plate 12, fig. 1). 



Experiment 151a. — Verbena ciliata, July 9, 1904. Prolonged darkness. Cutting in water, 

 placed in dark room at 6 p. m. ; starch in chlorenchyma and in guard-cells. 



July 10, 7 h 50 m a. m. Starch abundant in stomata; o to 3; 1 to 7; o to 3; 50 per cent 

 closed; no starch in chlorenchyma. 



i h 3o m p. m. Starch reaction in mature stomata as marked in control; reaction is not 

 equal in all stomata, and is more pronounced in young ones; 2 to 5.5 micra. 



July 11, 7 a. m. o to 3; o to 5; o to 2 micra, 90 per cent closed; starch plentiful in 

 mature stomata; absent from very young ones; smaller amounts in half-grown ones; none 

 in chlorenchyma; no oil. 



8 a. m. Cutting placed in strong diffused light. 



11 a. m. 2 to 5.5 micra. Very little starch in guard-cells, except in those of very young 

 stomata, which show a little; no starch in the chlorenchyma; no oil in the guard-cells. 



When stomata which are plentifully supplied with starch were subjected 

 to darkness, the starch was retained, so that even at the end of a period of 36 

 hours the quantity was not observably different from the amount in the 

 stomata of the control. They opened but little, if at all. When after pro- 

 longed exposure to the darkness such stomata were exposed to light at 8 a. m. 

 there followed, during the ensuing 3 hours, a reduction of the amount of 

 starch in the guard-cells. 



