ROLE OF THE STOMATA 



915 



has been the subject of study by several investigators, among them Iljin 

 (1923), Geiger (1927), Maskell (1928), Johansson and Stalfelt (1928), 

 Kostvchev, Bazyrina and Chesnokov (1928), Boysen-Jensen (1932), 

 Schoder (1932), Stalfelt (1935), Newton (1936), Heath (1939) and Heath 

 and Penman (1941). 



Of these, Kostychev, Bazyrina and Chesnokov (1928), and Schoder 

 (1932) could find no correlation between the two magnitudes. All other 

 observers concluded that, under certain conditions, a clear-cut relationship 

 can be noted between them. 



Thus, Maskell (1928) found a parallelism between the diurnal and seas- 

 onal course of stomatal apertures (as measured by a porometer) and the 



02468 U2468 



OPENING,/! OPENING,,! 



Fig. 27.8. Relation between photosynthesis and stomatal openings in ordinarj^ air 

 (0.03% CO2) (after Stalfelt 1935). One-sided illumination. Air flow 4 ± 1 m./min. 

 Average errors indicated by crosses. Ordinates, P in mg. CO-/(100 cm. 2 hr.). 



rate of photosynthesis. He made a theoretical estimate of the maximum 

 rate of carbon dioxide passage through the stomata, and concluded that it is 

 of the correct order of magnitude to operate as a bottleneck in photosyn- 

 thesis. 



Stalfelt (1935) determined the opening of the stomata by microscopic 

 measurements, using excised pieces of leaves of wheat or other cereals. 

 The same leaves also were used for the determination of photosynthesis. 

 The width of the stomata was varied by exposure to dry air, and preillumin- 

 ation by light of varying intensity. Figure 27.8 shows typical results. It 

 will be noted that in strong light (26,000 lux) the limiting effect of stomata 

 does not disappear even when they are fully open ; at 8000 lux, on the other 

 hand, this effect already ceases to be noticeable when the stomata are only 



