124 the; physiology of stomata. 



Experiment 204. — Verbena. Cutting placed in air deprived of CO2 at io h 30 m a. m., March 24, 

 1906. Normal: little or no starch in the guard-cells; entirely absent from many; 

 oil drops large; starch in small amounts in chlorenchyma. 



8 p. m., experimental part: o to 8 micra; amount of starch in guard-cells distinctly 

 greater and evenly distributed in the different stomata, though maximum amount is not 

 present. 



Experiment 205. — March 24, 1906. Cutting in air deprived of C0 2 in the dark at io h 30 m a.m. 



At 5 p. m., the results are identical with those of the foregoing experiment, 

 except as regards to the size of the pores, viz, 2 to 4 micra. 



Experiment 207. — Air deprived of CO2 in the light. Large bell-jar luted with vaseline, with 

 a vessel of potassium hydrate. Set up at 11 a. m., March 28, 1906. Starch abun- 

 dant in chlorenchyma, but none or meager amounts of starch in the guard-cells. Oil 

 present (plate 14, fig. 3). 



7 h3 m p.m. Starch very abundant in guard-cells, and present in the chlorenchyma; 

 o to 7 micra. Maximum temperature for the period: in the foliage 28°C; in bell jar, 30°C. 

 Temperature at 7 h 30 m p. m. i5°C. without and within (plate 14, figs. 4 and 4a). 



Summary. — If the stomata are exposed to air robbed of the C0 2 at the 

 time of minimum starch content, reformation of starch takes place as in the 

 normal. The starch in the chlorenchyma was undoubtedly that formed 

 earlier in the day. 



For the normal course of events on this day, see table 49, page 100, 

 March 26-28. 



Farmer & Chandler (1902) found that the stomata of Kalanchoe grown in 

 an atmosphere containing about 3.5 times the normal amount of C0 2 (11.47 

 parts per 1000) were gorged with starch and were always widely open, whilst 

 they were closed in the control. "This points to a permanent alteration of 

 form, seeing that the material throughout was killed and preserved in spirit." 

 They emphasized the point that in the plants treated with C0 2 the chloren- 

 chyma invariably shows an accumulation of starch, except in Kalanchoe, 

 which is a succulent, the succulents being noted by them as having a peculiar 

 physiology. In this plant, however, the stomata were gorged with starch, 

 a fact of significance. At first glance the greater amount of starch in the 

 stomata of the treated plant would appear to be due to a greater photo- 

 synthetic activity, but this conclusion does not follow of necessity. The 

 experiment, which was, however, designed for another purpose, does not 

 enable us to draw any conclusion as to the direct dependence of the guard- 

 cell upon the presence of C0 2 . The matter of a "permanent alteration of 

 form" may be seriously questioned. 



Francis Darwin (1898) concluded that "when illuminated, stomata remain 

 open in the absence of C0 2 ," and took issue with Schellenberg (1896), who 

 held the opposite view. The reason assigned by Schellenberg is that with 

 the loss of photosynthesis there is a consequent loss of turgor. Darwin con- 



