WATER LOSSES FRO:\r WET AREAS 59 



is plentiful and grows with its roots submerged in the shallow water 

 along the edges of stream channels and in swamps. It is a great 

 nuisance in drainage ditches. 



The triangular stem tule (Scirpus olncyi) is similar to the round 

 stem variety, being an aquatic plant that grows in areas of shallow 

 water. The stems are three cornered and grow with considerable 

 density, but are not generally as tall as the round stem tules. The 

 cat-tail {Typha lati folia) is a perennial marsh plant with flat leaves 

 that is frequently classed as a tule, although it belongs to an entirely 

 different family. Its cylindrical head is filled with thousands of small 

 cottony seeds which are spread by the wind. The cat-tail is found 

 wherever there is sluggish water. It spreads rapidly from seed and is 

 hard to eradicate. 



Both tules and cat-tails were grown in tanks set in the ground 

 with 2 inches of rim surface exposed. Water was held on the tank 

 surface to a depth of approximately 2 inches so that the roots were 

 entirely submerged. It seems probable that air is supplied to the root 

 systems of growths of this type through the coarse cellular structure 

 of the stems. The surrounding ground surface w^as free from vegeta- 

 tion during the first season, but later was covered with grass. 



All tule or cat-tail tanks were in exposed locations, subject to the 

 full effect of solar radiation and wind movement. In this respect, 

 tules grown at the stations differed from tules in swamps where a 

 certain degree of protection is afforded by increased vegetation and a 

 larger growing area. Consumptive use by swamp growth is partly 

 controlled by greater humidity overlying the swamp area. It is 

 probably true, too, that temperatures within the swamp are lower 

 than those outside. Both factors would combine to cause a lower use 

 of water by swamp plants than by those in exposed tanks. 



In general, it appears that aquatic plants in exposed tanks do not 

 attain the maximum height of stalk growth that is found under natural 

 conditions. Tank growth rarely exceeds 5 or 6 feet in height when 

 fully exposed, and more often is less, whereas natural swamp growth 

 of tules or cat-tails frequently grow to a height of 10 or 12 feet. The 

 highest growth occurs in the swamp interior, with shortej' stalks around 

 the water's edge. In this respect the outside growth in a swamp is com- 

 parable to that in experimental tanks. 



To determine whether size of tank had an effect on consumptive 

 use of water, an additional tank, 6 feet in diameter, was transplanted 

 to round stem tules at the Santa Ana station. The density of growth 

 at no time equalled that in the smaller tank and the consumptive use 

 per unit of area was consequently less. A comparison of the data 

 obtained from two tanks for tlie month of September, 1931, shows that 

 the smaller tank had a density of 87 stems per square foot of tank area, 

 which used water at the rate of 19.37 acre-inches per acre per month, 

 M-hilo the larger tank had only 57 stems per square foot of area using 

 12.43 acre-inches. The exposure of both tanks was identical. Carrying 

 the comparison further to determine the consumptive use per individual 

 stalk indicates that each tule used tlie same amount of water, regardless 

 of density of growth or size of tank in which it grew. Plate VIII-A 

 shows the 6-foot tule tank, No. 23, with the small tule tank. No. 19, at 

 the right. 



