234 



FLOWERS OF AQUATICS 



R. aquatilis, L. and R. divaricates ', 

 Schr. are also said to flower under 

 water, pollination occurring in a 

 bubble of air formed within the 

 perianth 1 . 



An Indian species of Podostemon, 

 P. Barberi, Willis 2 , has cleistogamic 

 flowers, with one stamen standing 

 close up against the stigmas (Fig. 82, 

 p. 121). Alisma natans* is described 

 as being cleistogamic in deep water, 

 while Echinodorus ranunculoides* has 

 an entirely submerged form which 

 flowers under water at a depth of three 

 feet. Other recorded cases of cleisto- 

 gamy are Heteranthera dubia 5 (Fig. 

 153) and Hydro thrix Gardner^ (Pon- 

 tederiaceae), Euryale ferox 1 (Nym- 

 phaeaceae), Illecebrum verticillatuwfi 

 (Caryophyllaceae), Tillaea aquatka* 

 (Crassulaceae), Trapella sinensis 9 (Pe- 

 daliaceae), and a number of species 

 of Lythraceae with apetalous or sub- 

 apetalous flowers, belonging to the 

 genera Rota/a, Peplis and Nesaea 10 . 



The pollination of cleistogamic 

 flowers, though it may occur beneath 



iRoyer, C. (1881-1883). 

 2 Willis, J. C. (1902). 

 3 Schenck, H. (1885). 

 4 West, G. (1910). 

 5 Wylie, R. B. (igi; 1 ). 

 6 Goebel, K. (1913). 

 'Goebel, K. (1891-1893). 

 8 Caspary, R. (1860). 



9 Oliver, F. W. (i! 



10 Gin, A. (1909). 



A B 



FIG. 153. Heteranthera dubia, 

 (Jacq.) MacM. A, L.S. through 

 an immature flower cut slightly 

 obliquely in the adaxial-abaxial 

 plane. The tip of the stigma lies 

 below the upper ends of the 

 anthers, and the style at this 

 stage is straight. B, upper por- 

 tion of an older flower cut in 

 the same general direction as A . 

 The stigma has been shoved up 

 into the upper end of the flower 

 in contact with the tips of the 

 anthers where the stigmatic 

 hairs touch the pollen grains 

 through the breaks in the sta- 

 mens. Pollen tubes are passing 

 from the anther into the stylar 

 chambers. The style is beginning 

 to fold on account of its exces- 

 sive elongation. [Wylie, R. B. 

 (I9I7 1 )-] 



