INTRODUCTION. 



staining, a similar number of stomata were measured in the strip and 

 the results compared. Table 1 gives in millimeters the results obtained 

 for alfalfa, which are typical of those obtained with other plants. 



TABLE 1. Results obtained from alfalfa. 



The results from alfalfa are given, since most of the experiments 

 discussed were performed upon alfalfa. At first this was due to 

 the fact that it was the most important plant susceptible to SO 2 

 injury. Later, its sensitive stomata and great availability made it 

 very useful in many of the series as a basis of comparison in the 

 study of the daily march of stomatal movement in other plants. 

 The results from the checks did not always agree as well as in the 

 above tables, but the agreement became greater as the number of 

 stomata measured was increased. The reason for trying to get as 

 nearly the same area as possible in stripping was not because of 

 any hope of getting the same stomata measured in the strip as on 

 the leaf, but because the effect of the great variation that often 

 exists in the stomata on the same leaf can best be avoided in this 

 manner. Table 2, showing the least amount of agreement in the 

 two sets of measurements of those made on alfalfa, will give the 

 reader a clearer idea of what is meant. 



In table 2 the agreement is not at all close. The second set of 

 10 measurements of stomata in the strip is closer than the first 10, 

 but when the two sets are averaged together, the result is 7.1 by 

 0.39, which is still nearer the average for width of pore. Had 20 

 stomata been measured in the leaf, the agreement would probably 

 have been quite close. Where there was much variation in size 



