36 MINNESOTA BOTANICAL STUDIES. 



being made at the tip, one at the midrib, and one near the base. 

 An average of the readings was taken for the number of stomata 

 found on the leaf in question. Measurements of the stomatal open- 

 ings were also taken when possible. 



The tables which follow have the measurements of the physical 

 factors above, immediately under which will be shown the behavior 

 of the plants with respect to their water loss. 



Individual Variation. 



The three following tables show the variation found in Helian- 

 thus plants grown and tested in the plant house under the same 

 physical conditions. All weighings were made in each series twice 

 daily, at six a. m. and at six p. m. The measurements were begun 

 February 25 and closed February 28, 1907. The plants in Series 

 I were eight weeks old, and had an average leaf area of 86.29 sq. 

 cm. Series II were five weeks old with an average leaf area of 

 28.658 sq. cm. Series III were three weeks old with an average 

 leaf area of 12.73 sq. cm. Only the cotyledons were developed in 

 this series, the true foliage leaves having just started. The num- 

 ber of stomata in Series I and II were practically the same. On 

 the upper side there were 270. on the lower side, 214. In Series III 

 there were 196. stomata on the upper side and 280 on the lower. 

 In all the tables that follow, water loss is given in grams, except 

 where otherwise indicated. 



The physical factors given are an average of several readings 



taken during the experiment, and are as follows : 



Light .59 



Temperature 61° 



Humidity 55% 



TABLE I. 



