A LONG-STALKED ELODEA FLOWER 



45 



It may be that the wide spread dioeeism in aquatic plants, evi- 

 dently recently acquired in some of them, is to avoid this di- 

 lemma. The writer has recently made a careful study of the 

 perfect flowers of Heteranthera duhia (Jacq.) MacM. and finds 

 them to be regularly cleistogamous. Whether deeply submersed, 

 the more favorable condition for vegetative growth, or near 

 enough to the surface to permit the flowers to open in air, fertil- 

 ization seems to take place uniformly before the flowers open. 



In the genus Elodea the flowers are generality functionally 

 monosporangiate though rudiments of the suppressed parts are 

 regularly present. The pistillate flower reaches the surface of 

 the water, if not too deeply submersed, through the elongation of 

 that portion of the epigynous flower above the ovary, — the "tubus 

 calicis" of the older writers, — i. e., it employs the principle of 

 flower elongation. 



The staminate flower of our common species of Elodea reaches 

 the surface by detachment. Each remains until fully developed 

 attached to the plant within the globose spathe. At maturity the 

 pedicil weakens and presently the flower is released, rises rapidly 

 the the surface and there sheds its pollen on the water. The sur- 

 face film of water has much to do with the floating of the pollen 

 and the general events of pollination in this plant.^ 



During the summer of 1909, in connection with work at the 

 Macbride Lakeside Laboratory on Lake Okoboji in northwestern 

 Iowa, the writer noted an unusual form of staminate flower on 

 the Elodea plants of that locality. The flowers were in striking 

 contrast to those of the common species in that they were carried 

 to the surface of the water on a long slender axis instead of re- 

 maining sessile and detaching at maturity (Fig. 1). Detachment 

 was subsequent to the shedding of the pollen, and was often long 

 delayed. It was interesting to encounter a pollen bearing flower 

 of Elodea employing the plan of axis elongation instead of de- 

 tachment, and to note within the one genus the occurrence of the 

 three possible modes of surface attainment. 



The staminate flowers of several South American species of 

 Elodea are reported to behave similarly. Caspary- describes cer- 

 tain species, among these, Elodea chilensis Casp. and E. calli- 



1 Wylie, Robert B., The Morphology of Elodea canadensis, Bot. Gazette, 37: 1-22, 

 1904, pp. 11-13. 



-Caspary, R., Die Hydrillen. Jahrb. f. wiss. Bot., 1: 377-513, ISoS, pp. 469-472. 



