Stomata , Leaf Water-content , and Wilting of Plants. 373 
and in this case the rate of wilting would be correspondingly slower. These 
circumstances would tend to displace the respective experiments from their 
position in Table II in the direction of the positions in which they are 
actually found. The aberration of Expt. 46 remains unaccounted for. but 
on the whole the series is consistent, and shows the close correlation 
between the air temperature and the duration of the preliminary acceleration 
period. Consideration of the stomatal aperture figures in Table II shows 
an exactly similar correlation existing between the air temperature during 
wilting and the duration of the preliminary period, with the reservation 
that Expt. 43 is again aberrant. This discrepancy is amenable to explanation 
as in the case of the transpiration results. This correlation between air 
temperature and the rapidity with which maximum stomatal aperture is 
reached has been observed and recorded in a less complete form by Laidlaw 
and Knight ( 16 ), and it is significant that a similar relationship has been 
found when studying transpiration rate. There appears to be no doubt 
that these maxima in the graphs of stomatal aperture and transpiration 
rate represent a definite stage in the physiological changes accompanying 
wilting. The more rapid attainment of these maxima which is associated 
with higher air temperatures is an indication that the plant is wilting more 
rapidly, and in fact, as Laidlaw and Knight suggested, the duration of the 
preliminary acceleration period is an indication of the rate at which the 
plant is wilting. 
Another point which may be considered in this connexion is the 
relation between the preliminary acceleration period of the stomata and 
that of the transpiration rate. Including the figures in Table II, there are 
available for comparison nine experiments in which complete records of 
stomatal aperture and of transpiration rate were obtained. In four of these 
the maxima of the two graphs appeared simultaneously, in five the maximum 
of transpiration was reached before that of stomatal aperture, and in none 
did the stomatal aperture maximum appear first. It must be pointed out 
that all the recorded figures are averages over periods of varying lengths, 
and that therefore, whilst an apparent difference between the times of the 
occurrence of the two maxima indicates a real difference, on the other 
hand apparent simultaneity does not necessarily mean absolute simultaneity. 
In the present experiments, had there been an interval of three or four 
minutes between the appearance of the two maxima, the chances are about 
even that this interval would have been overlooked. Therefore we may accept 
the five cases in which the maximum of transpiration rate was reached first, 
but we are unable to pass judgement on the other four. These five cases 
provide an instance of the influence of leaf water-content on transpiration 
rate, irrespective of the effect of stomatal aperture. During the period 
between the transpiration maximum and the stomatal aperture maximum, 
the transpiration rate diminishes although the stomatal aperture is increasing. 
