50 MINNESOTA BOTANICAL STUDIES. 



In order to get a more definite idea of the meaning of this table, 

 consider the average loss of a mature Hclianthiis anniius under sim- 

 ilar conditions. Scirpiis, with 135 stomata per sq. mm., during the 

 day lost on an average 74 mg. per sq. cm., while Helianthus, 

 having from 270 to 284 stomata on each side, showed an average 

 loss of 46 mg. 



From a study of the structure of Scirpiis it will be seen that it 

 possesses typical hydrophytic characteristics, (Clements, Research 

 Methods in Ecology, p. 126.). These characteristics are large inter- 

 cellular spaces, diaphragms, reduction in the number of stomata, 

 and lack of protection against excessive transpiration. A longi- 

 tudinal section of one of these stems shows the division into many 

 small chambers, with numerous cross partitions or diaphragms. An 

 attempt was made to estimate the total area of this interior tissue, 

 the total volume of the air-containing spaces, and to compare them 

 with the exterior transpiring area and the volume of the entire con- 

 ical stalk. 



Counts were obtained from the longitudinal section, and the aver- 

 age number of the cylindrical chambers was found to be 126. It was 

 calculated from cross sections, taken two inches apart from tip to 

 base of the entire stem, that the average number of chambers was 

 26, giving the total number of 3,276. 



At the same time the above counts were made, the average 

 length and diameter of each cylinder was determined to be 4.4 mm. 

 and .8 mm. respectively, thus making the total area of these cham- 

 bers 45,864 sq. mm. 



In addition to this inner transpiring area, the area of the dia- 

 phragm within each cylinder must be considered. These are com- 

 posed of thin layers of irregularly drawn out cells with large spaces 

 between them. In order to compute the amount of tissue in these 

 diaphragms, counts were made of the number in each chamber and 

 measurements of the area were made. The entire surface thus ob- 

 tained was 65,520 sq. mm., giving 111,384 sq. mm. total inner trans- 

 piring surface. Comparison of this with 7,479 sq. mm., convex sur- 

 face of the conical stalk, shows it to be fifteen times as great as the 

 exterior transpiring surface. 



Considering the volume of the entire Scirpus stalk and the vol- 

 ume of the intercellular air chambers, we find that .8 of the entire 

 volume is composed of air spaces. This extreme hydrophytic struc- 

 ture should be satisfactory explanation for the great amount of 

 water lost by this plant. 



