-xxiv 



lla. Leaves 2 cm. long or less CALLITRICHACEAE, p. 68. 



lib. Leaves thread-like, 28 cm. long 2a, in XAJADACEAE, p. 2. 

 lie. Leaves linear to elliptical, more than 2 cm. long 



Ib, in NAJADACEAE, p. 2. 



12a. Leaves in whorls of 3, abruptly widened at the base 



2b, in tfAJADACEAE, p. 2. 

 12b. Leaves in whorls of 3, widest near the middle 



Ib, in HYDROCHARITACEAE, p. 3. 



12c. Stems straight and erect, at leaves the flowers emerged; 

 leaves in whorls of 4 or more 2a, in HALORAGIDACEAE, p. 79. 



13a. Leaves with numerous small bladders attached, each bladder 

 13 mm. long LENTIBULARIACEAE, p. 105. 



13b. Leaves without bladders 14. 



14a. Leaves alternate 15. 



14b. Leaves opposite or whorled 18. 



15a. Delicate and rare plants growing attached to stones in running 

 water PODOSTEMACEAE, p. 48. 



15b. Plants 2 dm. high or more, with roots in mud or sand 16. 



I6a. Leaves once-pinnate 17. 



16b. Leaves 23 times pinnate 15b, in UMBELLIFERAE, p. 81. 



16c. Leaves palmately dissected 



Ib, in RANUNCULACEAE, p. 35. 



17a. Taste peppery or mustardy 34, in CRUCIFERAE, p. 45. 



17b. Taste not peppery or mustardy 



la, in HALORAGIDACEAE, p. 79. 



18a. Leaves pinnately compound 



3b, in HALORAGIDACEAE, p. 79. 

 18b. Leaves palmately compound 19. 



19a. Leaves opposite or in whorls of four -. 



119a, in COMPOSITAE, p. 123. 

 19b. Leaves in whorls of 512 CERATOPHTLLACEAE, p. 34. 



20a. Plants small, flattened, rounded or ovate, without distinction 

 of stem and leaf; the whole plant floating on or near the surface 



LEMNACEAE, p. 9. 



20b. Plant attached to the soil, with differentiated stem and 

 leaves 21. 



21a. Leaves on long slender stalks, which bear also a cluster of 

 slender tubers near the leaf-base; leaves heart-shape 



Ib, in GENTIANACEAE, p. 88. 

 21b. Leaf-stalks without a cluster of tubers 22. 



22a. Leaves all basal 23. 

 22b. Stem-leaves present 24. 



