52 



EFFECT OF PHYSICAL FACTORS AND PLANT CONDITIONS. 



between changes in the starch-content of the guard-cells and sto- 

 matal movement, but, as his graphs show, no midday closure oc- 

 curred and his curves are of normal light-induced movement only. 

 This type of movement has also been found correlated with changes 

 in the starch index, as the following series shows : Series 6 was begun 

 at 8 a. m. June 1, 1916, and ended at 9 p. m. the same day. At the 

 start the stomata were but 40 per cent open and did not reach maxi- 

 mum until noon. This slow morning opening was due to the heavy 

 clouds and a drizzling rain which lasted until Il h 30 m a. m. The 

 stomata remained at maximum until 3 p. m. At 4 p. m. they closed 

 to 75 per cent and at 5 p. m. to 50 per cent. No strips were then 

 collected until 8 p. m., when the stomata were found closed; they 

 remained closed to the end of the series. At the outset the starch 

 index dropped rapidly to the minimum between 11 a. m. and noon 

 and then rose slowly until 3 p. m. It then rose rapidly as the sto- 

 mata closed and continued rising to the end of the series. It still 

 showed a rapid increase at 8 and 9 p. m., although the stomata were 

 closed (fig. 27). The stomatal movement in Lombardy poplar was 



too 



90 



\ 



30 



10 



A 



/A 



c 



'\ 



\\ 



8 9 10 1 1 NOON I E34-S6789 



6 9 10 II NOON I 2 3 



Fia. 27. Series 6, showing movement in lower stomata FIG. 28. Series 7, showing movement 



of Lombardy poplar (A), and starch index in lower stomata of R. patientia (A), 



of the guard-cells (B), sunlight (C), humid- and starch index of the guard-cells 



ity (D), temperature (E). (B), sunlight (C), temperature (D). 



light-induced, not modified by any other factor, and was correlated 

 with changes of the starch index as Lloyd found in Verbena. 



Iljin found that when stomatal closure was induced by wilting, 

 the osmotic pressure of the guard-cells dropped and the amount of 

 starch in them increased. No such definite agreement could be 

 found, however, between midday closure and changes in starch- 

 content. In some series the amount of starch increased slightly 

 during midday closure, and this was quite noticeable when closure 

 was protracted. In others, no corresponding increase whatever was 

 found. Series 7, Rumex patientia, illustrates this. The upper sto- 



