RECENT ADVANCES IN SCIENCE 565 



assimilation and translocation. Hagen (Beitr. z. allg. Bot. 1, 

 261-91, 191 6) more definitely asserts that stomatal opening 

 results from sugar formation from starch in the guard cells. 

 Boysen Jensen (Bot. Tid. 36, 144-55, 1917) concludes that 

 the opening of stomata in some plants may cause an increase in 

 the transpiration rate which would otherwise be lower than 

 normal as the result of xeromorphic modifications. 



The purely physical side of the question of the stomatal 

 control of transpiration has been discussed and developed by 

 Jeffreys (Phil. Mag. 35, 270-80, 431-4, 1918) and Larmor 

 (Phil. Mag. 35, 350-52, 191 8). The question of the influence 

 of the activities of a stoma upon those of its neighbours is 

 approached, and whilst Larmor prefers to agree with Brown 

 and Escombe that interference is normally small, Jeffreys 

 maintains that with a normal size and distribution of stomata 

 on a leaf, the mutual effect is profound. He concludes that 

 only a small portion of the vapour pressure over a stoma is 

 maintained by that stoma, and that consequently the rate of 

 transpiration is not decreased by stomatal closure until a very 

 small aperture ( T V normal opening) is reached. This point is 

 said to reconcile the differences of the Darwin- Lloyd controversy, 

 but while it certainly may clear one statement of that dis- 

 cussion, it does not materially affect the two main contentions. 

 These two papers should provide a fruitful source of experi- 

 ment on evaporation and transpiration. 



* Bakke (Bot. Gaz. 66, 81-1 16, 191 8) has continued his experi- 

 ments on wilting plants and has confirmed his previous result, 

 in finding that permanent wilting occurs at a definite point, 

 namely when the water columns in the plant are broken. More- 

 over, this point can be readily determined by the sudden rise 

 in transpiring power as indicated by the hygrometric paper 

 method. During wilting a period is reached when the ratio of 

 day-transpiration to night-transpiration is unity, and the 

 duration of this period is probably an indication of the power 

 of the plant to resist water loss. Bakke is of the opinion that 

 the increase of transpiration following permanent wilting is not 

 due to the temporary stomatal opening reported by other 

 workers, and, indeed, it should be remarked that this opening 

 probably occurs long before the permanent wilting stage is 

 reached. 



Martin (Journ. Agr. Res. 7, 529-48, 1916) and Shive and 

 37 



