320 SMITH : APPLTC.ATTOX OF THE THEORY OF 



Francis Darwin in his paper "Observations on Stomata" 

 (-4) comes to the general conclusions — 



(1) That the nocturnal closure of stomata is not so com- 



plete as to prevent transpiration, but that it does 

 greatly diminish it. 



(2) That this degree of closure is extremely common in 



unspecialised terrestrial plants. 



Leitgeb (11) and Stahl (21) both found many plants with 

 open stomata at night and Leitgeb (11) went so far as to say 

 that as many plants have open as shut stomata at night, but 

 the very extensive researches of Darwin (4) led him to the 

 conclusion that in non-specialised plants there is a great 

 preponderance of nocturnal closure. Darwin is supported in 

 this conclusion by Schellenberger (17). 



It also seems clear from Darwin's work that in the daytime 

 different degrees of illumination have a marked effect in 

 producing different degrees of opening of the stomata. 



Measurements taken on the night of April 9th to 10th be- 

 come intelligible when the light factor is taken into account. 

 On this night the humidity of the air was considerably below 

 100 per cent, throughout the night, an unusual condition at 

 Hakgala. At 8 p.m. the humidity was 88 per cent, and de- 

 creased steadily to 75 per oent. at 2 a.m., when it increased up 

 to 90 percent . at r> \.\i. The growl 1 1. however, showed a steady 

 decrease from 1*2 cms. per two hours to "65 cms. per 

 two hours, and thus showed a close relationship to the steadily 

 foiling temperature curve and not to the curve of humidity. 



A humidity of 75 per Oenl . LS lower t han that recorded on some 



ninny days when the growth fell off owing obviously to lack 

 of sufficient water. Yet If our theory is to apply we must 

 suppose that the water supply is in exoess for the growth at 

 this temperature (14 C. to 9 < '.). even though I he same humi- 

 dity on other occasions iii the daytime obviously causes an 



insufficient supply of water. That this might occur seems pro- 

 bable when we COnsidei that ill the absence of light the 

 stomal sd, or oearrj so, and the comparatively Ion 



