

p 



1917] CURRENT LITERATURE 159 



Transpiration studies. — Among the more recent devices for the investi- 

 gation of the conditions affecting transpiration is the porometer devised by 

 Darwin, 11 which has attracted the attention of several workers, leading to 

 improvements by Balls 12 and by Jones 15 resulting in self-recording instru- 

 ments. Knight 1 * then somewhat simplified the device, and later, assisted 

 by Laidlaw, 1 * produced an automatic instrument that is probably better than 

 its predecessors for most forms of stomatal investigations. All agree in 

 measuring the stomatal opening by the rate at which air passes through the 

 stomata with a given pressure. A rather careful study by Knight 16 of the 

 methods to be employed in avoiding errors in the use of the porometer is sug- 

 gestive to future investigators in this field. Among the interesting results 

 obtained by this method there may be mentioned those of Darwin, and of 

 Laid law and Knight, who found indications that upon severing a leaf from 

 a stem and allowing it to wilt, a temporary opening of the stomata immedi- 

 ately preceded the closure accompanying wilting. 



■ 



In a recent investigation Trelease and Livingston 17 have made a com- 

 parison between the porometer and the standardized cobalt chloride paper 

 methods, and have obtained results showing a general agreement of data from 

 I the two. In the daily march of transpiring power the two are in close accord 



I during the morning hours up to about 8 :oo a.m., but from that hour until 11:00 



I a.m. the porometer index continues to increase, while the cobalt paper index 



*i tends to decrease. After 11 :oo a.m. the influence tending to decrease becomes 



evident in the porometer index also. This is taken to indicate that the poro- 

 meter measures the diffusive capacity of the stomata, but fails to take into 

 account other influences affecting foliar transpiring power. The divergence 

 J in the two records, therefore, may be an index of non-stomatal influences upon 



transpiration. On account of the limited data, these workers are not inclined 

 J to press this conclusion, but it appears to be an extremely probable suggestion. 



* 



IX 



Darwin, F., and Pertz, D. F. ML A new method of establishing the aperture 



of stomata. Proc, Roy. Soc. London B 84:136-154. 191 1. 



12 Balls, W. L., The stomatograph. Proc. Roy. Soc. London B 85:33-44. 1912. 



13 Jones, W. N., A self-recording porometer and potometer. New Phytol. 13: 

 353-3 6 4- i9 I 4- 



14 Knight, R. C, A convenient modification of the porometer. New Phytol. 

 14:212-216. 1915. 



15 Laidlaw, C. G. P., and Knight, R. C, A description of a recording porometer 

 and a note on stomatal behavior during wilting. Ann. Botany 30:47-56. figs. 3. 

 1916. 



16 KNIGHT, R. C, On the use of the porometer in stomatal investigation. Ann. 

 Botany 30:57-76. 1916. 



17 Trelease, S. F., and Livingston, B. E., The daily march of transpiring power 



porometer 



Jour. Ecology 



4:1-14. figs. 2. 1916. 



