1917] WYLIE—VALLISNERIA 145 



The writer would welcome photographs, drawings, or specimens 

 from distant regions for purposes of comparison. 



In conclusion, it seems clear that Vallisneria offers a remarkable 

 series of specializations mainly related to pollination at the surface 

 of the water. A few aquatic plants have solved the problems of 

 pollen transfer under water, and so may carry out their entire 

 life history as submersed plants. A good example is seen in Cerato- 

 phyllum demersum L., which is pollinated below the surface and so 

 may flourish at considerable depths in clear water. Neither Vallis- 

 neria nor Elodea shows any evidence of transition to subsurface 

 modes of pollination, although this would seem to be a desirable 

 goal for all aquatic flowering plants. On the contrary, they are 

 perhaps carried further and further from this possible habit by their 

 devices favoring pollination in air. Their specializations not only 

 bespeak long association with water, but also constitute a remark- 

 able series of adaptations to pollination at its upper limit through 

 the agency of the surface film. 



State University of Iowa 

 Iowa City, Iowa 





LITERATURE CITED 



1. Kerner, Anton, Pflanzenleben. Leipzig. 2:129-131. 1891. 



2. Wylie, Robert B., The morphology of Elodea canadensis. Bot. Gaz 

 37-" 1-20. 1904. 



3- Svedelius, Nils, On the life history of Enalus acoroides. Ann. Roy. Bot 

 Gard. 2:267-297. 1904. 



4- Wylie, Robert B., A long-stalked Elodea flower. Bull. Lab. Nat. Hist 

 State Univ. Iowa 6:43-52. 19 13. 



5- Cowles, Henry C, Textbook of botany. New York. 2:838. 1911. 



6. Lotsy, J. P.. Vortrage iiber botanische Stammesgeschichte. Jena. 3:642 



fig- 427. 1911- 



EXPLANATION OF PLATE IX 



A general drawing representing a group of associated flowers as they 



depression. 



depressed; free floating staminate flowers outside the 



