7 2 
Knight. — On the Use of the 
temperature. Only occasionally was a leaf found to be injured as a result 
of fixing the chamber ; after recovery from the first shock, leaves generally 
remained quite healthy with the chamber attached. 
Behaviour of Stomata of Different Regions. 
There is another question with reference to the porometer method 
which has been mentioned by Darwin and Pertz and also by Balls, viz. the 
relative condition of stomata on different parts of a plant. Porometer 
readings indicate stomatal changes only in the immediate vicinity of the 
leaf-chamber, and Darwin and Pertz quoted a set of readings from a plant 
of Primus laurocerasus , which showed marked differences in the size of the 
stomatal pores in leaves of different age. Balls proposed to get over the 
Fig. 6. Behaviour of stomata of different portions of a leaf under similar conditions. Ficus elastica. 
difficulty by fixing several chambers to different parts of the plant under 
observation, and by connecting them all to one reading apparatus, a mean is 
automatically obtained. In this case, however, each chamber should include 
approximately the same number of stomata, otherwise changes in the stomata 
beneath the chamber including the greatest number are liable to take an 
undue share in the total result. 
Experiments have been carried out on the behaviour of stomata on 
different parts of a leaf, and on different leaves of the same plant. 
i. A series of similar chambers were fixed to different parts of a leaf, 
and periodical readings taken from each. To determine the quantitative 
relations of stomatal aperture in the different regions, the reading per unit area 
for each chamber was calculated from the area of leaf exposed and the 
average reading over the whole period. 
