tqi4] OTIS— TRANSPIRATION OF WATER PLANTS 469 



favorable conditions, and rising stiffly above the water or bending 

 in graceful curves. The leaves are reduced to basal sheaths. 

 Seed is usually abundant, while vegetative propagation is secured 

 by perennial, creeping rootstocks. 



2. Scirpus americanus Pers. (three-square or chair-maker's rush) 



streams 



somewhat 



It does not form 



thick stands, as does the latter, but is sparingly placed here and 

 there. The culms are sharnlv three-angled throughout, with con- 



sometimes 



meter. The leaves are basal, narrowly linear. 1-3 



dm. long, usuaL^ rjr 



are long, stout, perennial. 



3. Pontederia cor data L. (pickerel 



The rootstocks 



treams, makin 



dm 



clump 



up several erect, long-petioled leaves and spikes of showy, blue 

 flowers to a height of 6-12 dm. The leaf blades are ovate to 



cordate-sagittate, 1-2 dm. long, and about one-half as wide at 

 the base. Stomata occur plentifully on the petioles and both sides 

 of the leaves, but they are somewhat more numerous on the lower 

 than on the upper sides of the blades. Propagation is secured 

 by an abundance of seed, but chiefly by thick, creeping, perennial 



rootstocks. 



4. Sagittaria latifolia Willd. (arrow-head) inhabits only the 

 shallowest water and muddy banks of lakes, ponds, and rivers, 

 usually in solitary clumps and seldom covering any consider- 

 able area. The leaves are basal, lorig-petioled, arising from 

 tuberous or fibrous rootstocks to a heierht of 6 dm. or more. The 



in 



always sagittate. Stomata occur sparingly on the upper surface of 

 the blade and on the petiole, but are only moderately abundant 

 beneath. 



5. Acorns Calamus L. (sweet flag) is rather infrequently found 

 along the margins of streams in water as much as 4-6 dm. in depth. 

 The narrow, sweet-scented, swordlike leaves arise from the thick, 



