24 Rhodora [FEBRUARY 
moistening of the ripe spores while yet submerged; for this, as we 
have seen, would lead to their sinking or release. * * * * 
'The pistillate flower, as has been noted above, reaches the surface 
of the water by the lengthening of the fused parts above the ovary. 
* * * "The floral parts * * * * are repellent to water and 
so resist wetting for many hours. With the opening of the flower 
the three prominent stigmas quickly recurve, arching well out over 
the floral envelopes. Lying thus, commonly on its side at first, 
the weight of the flowers rests chiefly on the stigmas. Since the 
stigmas are not readily wetted by water, they form a depression in 
the surface film. Pollen grains floating near the flower therefore 
approach and quickly slide down into contact with the stigma. 
There is thus established about each flower ‘a circle of influence,’ 
which in quiet waters is about 2 cm. in diameter, and spores floating 
into this area are immediately brought into contact with the stigma. 
* * * * 
It will be seen that the whole process of pollination is dependent 
in one way or another upon the surface film of water." 
Later this species was observed during two successive seasons by 
R. W. Woodward, and he gives a detailed, accurate description! of 
the gross morphology of the staminate and .pistillate flowers, and 
comments on the mechanism of cross fertilization of this dioecious 
specles. As he points out, the pistillate flowers are borne from 
spathes in the upper axils that sheathe the base of the long floral tube 
which elongates and pushes the flower bud to the surface of the 
water. In the fresh material Woodward observed staminodia, thus 
demonstrating that E. canadensis differs in the morphology of its 
flowers only in the absence of staminate flowers. The staminate 
flowers of E. occidentalis are tiny globose affairs about 2 mm. long 
sessile in the middle or lower axils. "The staminate spathe encloses 
the flower tightly, and may be prolonged into a short apiculate tip. 
Rydberg distinguished Philotria Nuttallii (Planchon) Rydb.,? an- 
other species which has its floral structure similar to the preceding. 
It was launched by Planchon as a doubtful species based on Udora 
canadensis Nutt.,? excluding the synonym Elodea canadensis Michx. 
Rydberg takes it up for “plants referred to Elodea canadensis Michx., 
1 Ruopona xxi. 218 (1919). 
? Bull. Torr. Bot. Cl. xxxv. 461 (1908). 
3 Nuttall, Thomas, Gen. N. Am. Pl. ii. 242 (1818). 
