DAILY MOVEMENT IN ALFALFA. 



21 



leaves on the plant showed the stomatal apertures to check with those 

 found in the strips taken at the same time. This left no doubt as 

 to the actual occurrence of the mid-day closure. Moreover, since 

 this curve does not resemble either of the previous curves, it adds to 

 the evidence that, in alfalfa at least, the course of stomatal opening 

 varies greatly from day to day. 



On May 23, 1916, another series was made with these same plants, 

 starting at 10 p. m. and ending at 8 a. m. the next day, while on 

 May 29, 1916, a complementary series was begun at 8 a. m. and 

 ended at 10 p. m., thus furnishing a composite 24-hour series. It 

 was hoped to find from the first whether the stomata remained 

 closed all night, and at what time they opened in the morning. 

 The night of May 23 was cold, clear, and rather windy. The hu- 

 midity was not high, averaging only 45 per cent. The day of May 

 29 was clear, sunny, and warm, reaching 83.5F. at 3 p. m., but 



- MAY Z4 



H 1* 

 too 



10 II MT. I 23*5676 



9 10 II NOON I 234-56 769 10 



FIG. 5. Composite series 45, showing movement in upper stomata of alfalfa 

 (A), sunlight (B), temperature (C), humidity (D). 



after sunset the temperature dropped quickly to 58 F. at 10 p. m. 

 The stomata were closed at 10 p. m. when series 4 started and re- 

 mained closed until midnight. At 1 a. m. they were 5 per cent open; 

 at 2 a. m. they were 10 per cent open; but they closed again the 

 following hour. The sun appeared at 5 h 20 m a. m. and no further 

 opening was observed before this time. At 6 a. m. they had opened 

 to 10 per cent, at 7 a. m. to 30 per cent, and at 8 a. m., when this 

 series closed, they were half open. At the beginning of series 5, 

 on May 29, they had opened to 60 per cent at 9 a. m. and con- 

 tinued opening uniformly to maximum at 11 a. m., in which condition 

 they remained until 1 p. m. At 2 p. m. they were closed, a change 

 of 100 per cent occurring within the hour. At 3 p. m. they had 

 opened to 80 per cent and, except for a slight closure at 4 p. m., re- 

 mained in this condition until 5 p. m. They then started to close 

 gradually for the day, the process being gradual and rather uniform 

 and not completed until after 9 p. m. (fig. 5). 



