STOMATA AND CARBON DIOXID. 121 



"less resistant" than the epidermal cells, losing their turgor earlier, may be 

 applied to much prolonged darkness, unless there is something going on within 

 the guard-cell to keep up the supply of osmotic materials beyond the amount 

 occurring in the epidermal cells. The point will be referred to later. 



EXPERIMENTS WITH AIR FREE OF CARBON DIOXID. 



BEGINNING AT SUNRISE. 

 Experiment 167. — Verbena ciliata, in air deprived of carbon dioxid. July 15, 1905. 



A good-sized sprig was placed, shortly after sunrise, at 5 h i5 m a. m., under a 

 bell-jar, together with a vessel of strong potassium-hydrate solution offering 

 a large surface to the air. The whole was exposed to the light, but the interior 

 kept at normal temperature by means of a wet cloth on the outside of the 

 bell-jar. Starch abundant and oil absent from the guard-cells. 



July 15, 8 h 40 m a. m. Control piece: Oil present, starch abundant in 

 chlorenchyma ; a small amount of starch in the guard-cell plastids. 



Experimental piece : Oil absent, excepting in very small droplets in some 

 cells; no trace of starch in the majority of guard-cells, although in very young 

 stomata there is plenty of starch; starch absent from the chlorenchyma cells. 



July 17, 9 a. m. The cutting taken at sunrise on July 15 has been kept 

 under the bell- jar till this time, *. e., for 52 hours, during the day time in the 

 diffused light of the laboratory ; starch absent from chlorenchyma but pres- 

 ent in abundance in guard-cells, from which, however, oil is absent. (C/. 

 experiments 201a and 2016, which gave similar results.) 



Experiments 201a and 201b. — March 17, igo5. Cuttings of Verbena placed in bell-jar in 

 air deprived of CO2 and (a) placed in the light, (b) placed in the dark. Set up at 

 5 h 30 m a. m. Oil in large drops in guard-cells or entirely absent. (See table 53.) 



Conclusion. — Starch disapp2ars from the guard-cells in the absence of C0 2 

 in the light, as it does normally; it is not formed in the chlorenchyma. Oil 

 is apparently not formed as uniformly, although it occasionally appears. The 

 stomata opened. In the dark, in absence of C0 2 , the starch is not removed 

 from the guard-cells, nor does oil appear in them. Starch is not formed in 

 the chlorenchyma, as is to be expected. 



Experiment 209. — March 2q, 1906. Cutting placed under bell-jar in air — CO2 at 5 h 30 m 

 a. m. The condition of the air in the bell-jar was controlled by potassium hydrate and 

 lime water; concluded at ii h 3o m a. m., bell-jar 25 to 30 C. 



5 h 30 m a. m. Normal; starch present in abundance in guard-cells; absent from many 

 chlorenchyma cells, but found in small grains in many; o to 3 micra; plastids large. 



11^30™ a. m. Normal; oil drops, usually 2 in guard-cells, and of good size; 4 to 8 micra; 

 starch in small amount in the guard-cells; plentiful in the chlorenchyma; plastids small. 



Experimental: No oil; 6 to 8 micra; starch in small amount in the guard-cells, but none 

 in the chlorenchyma.* Plastids small. 



*The occurrence of starch in the stomata in the 111130m material, similar amounts in 

 both experimental and control, is due, I believe, to the fact that the material was, unavoid- 

 ably, not taken at the critical period. 



