Experiment 154.-Verbena, July 10, 1905. Cutting placed in the dark room at 8h551 a. m. July 10, 8h55m a. m. Starch in very small amount, appearing as minute granules in the pale plastids; 5.5 to 10 micra.

10h30m a. m. No increase of starch observable; 2.8; 2.8 to 5.5 micra. Control: 2.8 to 7; 4 to 7; 2.8 to 5.5 micra. Little if any increase of starch observable. 1h15m p. m. Small increase of starch; if anything more in the dark-room plant than in the control. Abundant starch in the chlorenchyma of control, but in the experimental plant no more than at 8h55m a. m.; 2 to 5 micra. A few extreme measurements: closed and 5.5 micra; control, o to 3 micra.

July 11, 8 a. m. 2 to 5.5; 0 to 5 micra. Comparison with the control shows a distinctly greater starch content in the guard-cells of the experimental plant. Experimental cutting placed in strong diffused light at this time.

11h 20m a. m. Closed; o to 3; 0 to 4 micra.

The younger stomata are those chiefly

closed, while the mature ones are usually open to 2 to 4 micra. Very little starch in the mature stomata, but considerable amounts in the young ones. The specimens taken turned out to be rather young and had in consequence a large number of undeveloped stomata. The large proportion of closed stomata is attributed in part to this. Starch granules in the chlorenchyma quite obvious.

Experiment 155.-July 11, 1905. Cuttings placed in the dark room at 8h35m a, m. July 11, 8h15m a. m. Control: Little starch in guard-cells; oil present.

8h35m a. m. Control: No starch in guard-cells; oil bodies at maximum; cuttings placed in the dark; control pieces taken also from the cuttings showed no starch in guard-cells, and oil drops large; starch in chlorenchyma; 4 to 9; 2.8 to 8.4; 2.8 to 8.4 micra.

July 12, 8h50m a. m. No oil drops; starch abundant in guard-cells in large granules, the plastids appearing wholly stained with iodine; none in the chlorenchyma; o to 2.8 (7) micra, 80 per cent closed; o to 4 micra, 70 per cent closed.

I p. m. Starch still present in guard-cells.

July 13, 8 a. m. Only an occasional stoma has starch; 90 per cent closed, the rest open to a slit of 1 or 2 micra; no starch in chlorenchyma; in malformed guard-cells a large amount of starch is to be found, and this is true also of perfect guard-cells when they are paired with imperfect ones. Part of the material placed in the strong diffused light of a north window at this time (8 a. m.) with the following results:

9h45m a. m., in diffused light. Minute granules have appeared in the chlorenchyma, but none as yet in the guard-cell plastids.

12h15m p. m. in diffused light. Stomata closed, save for a few which are opened to a slit of 1 or 2 micra; the plant is partly wilted; stem trimmed; stomata of leaves which are submerged in the water of the vessel in which the cutting stands are widely open, but no starch is to be seen in them.

3 p. m. in diffused light. Distinctly deeply-stained starch grains in the chlorenchyma; a small amount in fine granules in the guard-cell plastids.

6 p. m. Light. A distinct increase of starch in the guard-cell, though not abundant. July 14, 7 a. m. Part of experimental material, after 3 days in the dark room, has stomata ranging from o to 4 micra in width, 50 per cent being 2 micra; starch content of guard-cells varies from a little to abundance; none in chlorenchyma.

Summary of 144, 154, and 155.-When material is taken at the time of minimum starch content, maximum oil content, and maximum opening, and placed in the dark the oil apparently does not reappear. Starch increases during the first 24 hours, and shows a decrease at the end of 48 hours. In the

Stomata of Verbena ciliata in darkness.
Experiment 210.

2. Two plastids showing extremes of starch content at 6 a. m.

3. A group of stomata, 11 a. m., January 11.

Experiment 210.

Starch is absent from the mature stomata, a, b, and d, but is present in abundance in the young ones, c and e (figures 6 and 7).

4. A mature stoma containing no starch, 11 a. m., January 11.

5. Stoma at 11 a. m., January 12, after 24 hours of darkness. Cf. figure 4, which is the control.

6 and 7. Young stomata containing an abundance of starch.

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. Α 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 activity 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 5h30m a. m, and placed in dark.

5h 30m 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 photosynthesis. (See also experiment 209.)

11h30m 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 p. m.; starch in chlorenchyma and in guard-cells.

July 10, 7h50m a. m. Starch abundant in stomata; o to 3; 1 to 7; 0 to 3; 50 per cent closed; no starch in chlorenchyma.

1h30m 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; 0 to 5; 0 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.

II 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 prolonged 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.

The stomata, being less than half open at the beginning of the experiment, remained so, though closures become more pronounced during 36 hours. Placed, at the end of 36 hours, for 3 hours in diffused light, a measurable though not a great amount of opening movement occurred, while the starch was reduced.

Experiment 221.-Verbena ciliata, April 27-May 3, olla, and irrigated; twig kept in dark for 6 days.

19c6. Twig in situ covered with an Set up on April 27, 1907, at 6 a. m. April 30, 6 a. m. Oil drops small but normal; stomata closed, or a mere slit; starch absent from chlorenchyma; starch present in guard-cells in meager but variable amount; sometimes plentiful; three examinations; the last with KI+I, 1/16 oil imm., oc. 3.

Experimental part: Starch in guard-cells absent or in very minute quantities; none in chlorenchyma.

May 3, 6 a. m. Oil drops as before, viz, small or not evident; no evidence of starch in guard-cells or chlorenchyma; an occasional stoma 3 miera in diameter; others closed. Control: Starch abundant in guard-cells; a little in the chlorenchyma.

II a. m. Control (see experiment 219).

Experimental part: No starch in the guard-cells or chlorenchyma.

The following three experiments were carried out to determine especially if oil accumulates in the guard-cells in the dark:

Experiment 160.-July 14, 1905. Taken at 6h50m a. m., at which time no oil drops were visible; starch in guard-cells in fine granules; 2 to 5, mean about 4; 2 to 11; mean about 6 to 7 micra (the latter piece had very large stomata).

11h30m a. m. micra.

Control: Oil drops large; no obvious change in starch content; 8.5 to 14

• Experimental part: No oil visible, nor change in starch content; 2 to 6; 2 to 8.5; 4 to 8 micra.

No oil was formed in the dark during the period when, under normal conditions, this occurs. The similar amounts of starch in the control is shown by other experiments not to be due to the absence of change in the amount, but to the return, after the minimum, which occurs about 8 to 9 a. m., to the increased, but not maximum amount.

5h30m a. m.

Experiment 168.-Verbena ciliata, July 15, 1905.

Cuttings placed in the dark room. 5.5 to 8; 2.8 to 8.5 micra; no oil drops. 9h40m a. m. Starch plentiful in guard-cells, but no oil drops; no starch in chlorenchyma; 2.8 to 7 micra, a few with openings 8.5 micra.

Control: 5.5 to 8.5 micra; oil present.

Experiment 202a.-Verbena ciliata, March 17, 1906.

5h30m a. m. Cuttings placed in the dark room. Starch abundant in guard-cells; absent from chlorenchyma; no oil in guard-cells.

II a. m. Control: Starch absent from guard-cells; abundant in chlorenchyma; oil drops large in guard-cells.

Experimental part: Starch present in guard-cells; absent from chlorenchyma; no oil. (See experiment 2014.)