I 



51 



Cattails and tules were grown in tanks at the Santa Ana 

 station, the ground surface of the tank being submerged as in a 

 swamp. Air probably is supplied to the roots through the coarse 

 cellular structure of the stems and not directly through the soil. 

 Ground surrounding the tule tanks was free of vegetation during 

 the first season but later was covered with grass. 



Cattail and tule tanks were in exposed locations, subject 

 to the full effect of solar radiation and wind movement. Tules 

 grown in tanks differ from those in swamps where protection is 

 afforded by surrounding areas of similar growth, lower tempera- 

 tures, and greater humidity. These factors have a controlling 

 influence on the quantities of water consumed by the plants with 

 the result that water transpired and evaporated by swamps is con- 

 siderably less per unit of area than that used by similar growth 

 in exposed tanks. Aquatic plants in tanks do not attain the max- 

 imum growth found in swamp areas. Tule growth in isolated tanks 

 rarely exceeds 4 to 6 feet in height. Maximum growth occurs in 

 the swamp interior with shorter stalks around the edge of the 

 water, and in this respect the exterior growth is comparable to 

 that in experimental tanks. 



Because of abnormal exposure, consumptive use of water by 

 tules at Santa Ana was excessive. Round-stem tules used more 

 water than cattails, possibly because of greater density of growth. 

 Their consumptive use was frequently 1 1/2 inches per day, and at 

 one time averaged an inch a day for a period of 6 weeks. The use 

 of water for the year ending April 30, 1931 was nearly 178 inches 

 or 269 per cent of the evaporation from a Weather Bureau pan. 

 Data on use of water by tules and cattails grown in exposed tanks 

 at Santa Ana are given in Table 8. These data do not represent 

 consumptive use under normal swamp conditions but are given here 

 to show the extreme results which may be obtained under xinnatural 

 conditions. Without adjustment they are not applicable to swamp 

 conditions. 



Nevertheless, all tules and cattails do not grow in 



