1904] WYLIE: ELODEA CANADENSIS 13 
The pistillate flower, as has been noted above, reaches the 
surface of the water by the lengthening of the fused parts above 
the ovary. Elongation does not cease immediately upon reach- 
ing the surface, as there is usually developed some surplus 
length before the floral parts open. These parts are repellent 
to water and so resist wetting for many hours. With the open- 
ing 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 upon 
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 con- 
tact with the stigma. There is thus established about each flower 
‘“‘a circle of influence,” which in quiet waters is about 2™ in 
diameter, and spores floating into this area are immediately 
brought into contact with the stigma. When numerous, pollen 
grains may form a layer lining the bottom of the depression. 
If at such a time the flower is submerged, as may happen from 
wave action, etc., the surface film binds together floral parts and 
spores as they pass beneath the water, and invests them with a 
considerable volume of air. When all again come to the surface 
the pollen grains may be seen sprinkled over all parts of the 
flower including the other stigmas. Spores lodged against any 
part of the flower may in this way be transferred to the stigmas. 
It will be seen that the whole process of pollination is depend- 
ent in one way or another upon the surface film of water: (1) 
such a film makes possible the accumulation of oxygen bubbles 
within and above the staminate flowers, with whatever of advan- 
tage that may follow; (2) it is directly responsible for the float- 
ing of the pollen grains on the surface of the water; (3) the 
surface film brings the floating pollen grains into contact with 
the stigmas of the pistillate flower. 
THE POLLEN TUBE, 
As might be expected, considering the remarkable morphol- 
ogy of the pistillate flower, the study of the pollen tube was not 
without interest. These growths not only have great length, 
5-30, but are quite large and display some unusual activities. 
