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IQI7] 



W YLIE— VA LLISNERIA 



143 





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certainty, provided both kinds of flowers are near together in the 



I 



same body of water. No doubt the pollen-bearing flowers often 

 ride the surface of the water for considerable distances. They 

 will float for days, and the pollen seems to withstand desiccation 

 for a long time. In our laboratory aquaria the decline of micro- 

 spores seems to be due to the attacks of fungi, and collections from 

 the field often show hyphae among 

 the spores. 



From 200 to 450 ovules line the 

 walls of the ovary, so that the entire 

 pollen output of several staminate 

 flowers would be necessary for fer- 

 tilization, even if all the spores germi- 

 nated. Fertilization seems to take 

 place with certainty, for few ovules 

 fail to develop into seeds. Scores of 

 supernumerary pollen tubes are fre- 

 quently seen lining 



the walls or 

 wandering through the ovarian cham- 

 ber among the ovules. Many of these 

 meandering pollen tubes form enlarge- 

 ments at their distal ends similar to 

 those previously reported for Elodea 

 canadensis (2). 



Fig. 5. — With further depression 

 the water has closed over the 

 flowers, now shut together in a 

 common bubble; out-turned bases 



Turning now to KERNER'S widely of staminate flowers may be seen 



Copied figure illustrating his descrip- on all sides, while pollen masses are 



, : * . , lt . r T r ii- • being pressed directly into stigmas; 



tion of the pollination of Valhsneria near by are ^ ^^earing 



Spiralis, one is Struck by the many flowers that escaped when others 



points of contrast with the foregoing were caught in the bubble (these 



account. His illustration shows a 



• •[•. 



ved during time of exposure 



pistillate flower 



with long 



slender 



and so are blurred in picture). 



ovary which, relative to the spread of the floral parts, is only about 

 one-third of the diameter of that in our form. The spathe invests 

 only the base of the ovary, whereas in ours it extends up almost to 

 the sepals. The wide-spreading sepals are shown as straight, while 

 the broad stigmas are flattened, outstanding, and raised entirely 

 above the surface of the water. The stigmas, as shown in the 



