DAILY MOVEMENT IN CEREALS. 



41 



showed 16 per cent opening at 9 a. m., 6 per cent at 10 a. m., and 

 showed closed stomata after this time, as in barley (fig. 22) . Although 

 conditions were different, the stomata of barley behaved in the same 

 manner as in the first series. However, it is improbable that such 

 similarity would have been found throughout had the two series been 

 complete. Other experiments have shown that low morning temper- 

 ature has an inhibiting effect upon opening of stomata. 



Wheat, oats, and barley were included in series 10, June 8 and 9, 

 1916, together with alfalfa and potato, the stomatal movements of 

 which have already been described in detail. The day was clear 

 and fairly warm, the highest temperature (88 F.) being reached at 

 2 p. m. (fig. 7) . Because of the low humidity, the evaporating power 

 of the air was high, and in consequence all the plants faced the danger 

 of excessive water-loss. The stomata of alfalfa were closed for a 

 longer period during the day and hardly showed maximum opening 

 at all. Potato, on the other hand, had stomata open widely all day 

 and most of the night. The cereals did not have the high water- 

 content in their plots that the potato had, and it is doubtful whether 

 their roots had been able to follow the rapid dropping of the water- 

 table to 6 or more feet. Hence the water-content of 16 per cent 

 found at a depth of 2 feet probably represented the highest amount 

 within reach of the roots. Barley showed only a small fraction of 

 maximum stomatal opening during the first 3 hours of daylight and 

 closure during the remainder of the series. The greatest opening 

 occurred at 7 a. m., but was only 9 per cent. The stomata of wheat 

 remained open until after 10 a. m., as did the stomata of oats, but 

 while wheat reached 22 per cent opening at 7 a. m., that of oats was 



7 8 9 10 II NOON I 



8 9 IO II MT. I 



FIG. 23. Series 10, showing movement in lower stomata of wheat (A), barley (B), and oats (C). 



only 9 per cent. In none of these plants was there any indication 

 whatever of night opening. The results show that wheat was appar- 

 ently more able to withstand the adverse effect of higher tempera- 

 tures and the high evaporating power of the air than either oats or 

 barley. Series 7 and 8 show that the stomata of barley do not open 

 as widely or as long when the temperature rises above 75 to 80 F. 

 Further evidence of this is found in series 11, begun at noon June 

 19 and ended at 2 p. m. June 20, 1916. Among the sets of epiderm 

 collected was one each of wheat, oats, barley, corn, and millet. The 

 maximum temperature reached on June 19 was 79 F. and on June 

 20, 76.5 F. The humidity was rather high for the region, as it at 



