26 



PUBLIC HEALTH BULLETIN NO. 286 



4. Plants floating on surface 5. 



4. Plants floating just below water surface; plant Wolffiella, p. 103. 

 body made up of a clump of short filaments 

 (fig. 3). 



5. Plant body of small overlapping scales (fig. 4) Azolla, p. 67. 



5. Plant body simple or compound, made up of rounded 6. 

 floating leaves. 



X I'/? 



xl'/? 



Figure 3. 



FlOURE 4. 



6. Plants simple, extremely minute, appearing as Wolffia, p. 103. 



grains on surface of water (fig. 5) . 

 6. Plants compound, made up of several rounded- 7. 

 oblong disk-like bodies, floating on surface of 

 water. 

 7. Plant body inconspicuously nerved, rootlets 1 per disk Lemna, p. 103. 



(fig. 6). 

 7. Plant body conspicuously nerved, rootlets 2 to several Spirodela, p. 104. 

 per disk (fig. 7). 



X 8 



FlQURB 5. 



X I'll 



Figure 6. 



Figure 7. 



