STOMATA AND CARBON DIOXID. 123 



The formation of oil may be connected with the high temperature which 

 occurred in the bell- jar, which was 15 F. higher than outside. 



EXPERIMENTS COMMENCING AT TIME OF MINIMUM STARCH CONTENT OF 



THE GUARD-CELLS. 



Experiment 161. Verbena ciliata, July 13, 1905. A shoot remaining attached to the 

 experimental plant covered by a bell-jar, and a vessel of potassium hydrate introduced . 

 The interior temperature kept normal by wet paper on the outside of the bell-jar. 



9 h 2O m a.m. Temperature, 31 in bell -jar; starch in guard-cell plastids in minute granules; 

 stomata open wide; otherwise as in experiment 162, at the same hour. 



9 h 45 m a. m. Temperature, 30.5 in bell-jar. 



I2 h 45 m p. m. Temperature, 30.5; oil present in a few cells; little or no change appar- 

 ent in the starch content of the guard-cell plastids, if anything a little more ; no observable 

 difference between experimental and control leaves. 



Conclusion. Oil disappeared slowly ; starch formed slowly if at all ; change 

 not marked in 3 hours. 



Experiment 162. Verbena ciliata, July 14, 1905. A good -sized cutting was placed under a 

 bell-jar, together with a vessel of potassium-hydrate solution, with large surface 

 exposed. Set up at 9 h 3o m a. m. 



9 h 20 m a. m. Starch in minute granules in the guard-cell plastids; oil drops large; pore 

 4 to 8 micra wide, mean about 6 micra; starch in chlorenchyma abundant. 



5 h 45 m p. m. Starch abundant in guard -cells, but no oil; the guard-cells of control con- 

 tain perhaps a trifle more starch; openings 4 to 8 micra wide; when placed in water they 

 open to 8 to n micra; starch in chlorenchyma much reduced. 



July 15, 5 a. m. Starch in guard-cell plastids very abundant, and the grains so large 

 that they cannot be delimited from each other; no oil; starch in chlorenchyma; openings 

 o to 8.5 micra. Of the material taken for examination, one large piece shows many stomata 

 closed entirely, but about 10 per cent rather widely open (8.5 micra); another piece shows 

 the same range of size, but with numerous intermediate sizes. In the various pieces a few 

 stomata are found as wide as n micra. 



In carrying out the above experiment the temperature was kept normal 

 and fairly constant by keeping wet a jacket of thick bibulous paper on the 

 outside of the bell- jar. The whole was exposed to strong diffused light. 



Conclusion. In absence of CO 2 the oil disappears; starch is formed to, 

 or near to, the maximum amount in 8 hours. In this instance closure of 

 stomata was not prompt. 



Experiment 203. 



A cutting, taken on March 17, 1906, at io h 3O m a. m., was placed in CO 2 - 

 free air and allowed to remain for 52 hours. At the close of the period the 

 stomata in general did not contain starch. Starch is, however, found in 

 abundance in those stomata which lie near to the vascular strands. 



Experiment 2030, March 19, 1906. 

 Duplicate of 203, giving identical results. 



