74 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
seeds below the surface, although the flowers are borne on emersed peduncles and 
have no adaptation for water fertilization. In the well-known case of Vallisneria 
spiralis the water assists in fertilization. The male flowers are borne on scapes at 
the base of the plant. When the inclosing spathe ruptures, the flowers rise to the 
surface and float about until they come in contact with the stigma of the female 
flower, to which some of the pollen adheres. After fertilization, the female flower 
is drawn below the surface, where the seeds ripen. 
Our knowledge of the germination of the seeds of aquatic plants is still very 
fragmentary. The seedlings of rootless aquatics show the greatest departure from 
land forms. In Ceratophyllum a short radicle is developed, but it never grows out 
into a primary root, nor are other roots formed. In the Potamogetons and other 
rooting species the special adaptations for an aquatic existence in the seedling are 
not so marked. A primary root is developed, which later perishes and gives place 
to adventive roots. 
Kolpin Ravn 1 has studied the power of seeds of aquatic and marsh plants to float 
and he finds that most seeds are heavier than water and thus can not float unless 
adhering in masses; or they may not be easily wet, when they will float in spite of 
their weight. Some float but a few days and their distribution is local. Many seeds, 
however, are doubtless carried by currents and water fowl, although the seeds of 
true aquatics are not well adapted to spread by animal agency, and it is probable that 
waves, floods, and water currents are more important in this respect than animals. 
The active vegetative propagation and the perennial character of water plants 
have tended to reduce the importance of seed production. Many aquatics produce 
seed much less freely than land plants and in some seed production occurs but seldom 
or has never been recorded. Ceratophyllum , Elodea , and Lernnaceoe may grow for 
years in one locality and never produce seed. Potamogetonrobbinsii is not known to 
seed. I n the Put-in Bay region I was unable to find Potamogeton amplifolius in fruit, 
and fruits were scarce on P. zoster cefolius, P. pusillus , and P. freisii. The last three 
propagate by winter buds, and are perhaps losing the power to produce seed. 
BUDS AND OFFSETS. 
Besides rhizomes water plants propagate vegetatively by simple offsets and pass 
the winter by various means. Almost any fragment of a plant of Elodea when .in 
water may continue to grow and produce a new plant. The same is true of Cerato- 
phyllum , Utricularia , many Potamogetons , Myriophyllums , etc. 
Some species pass the winter unchanged at the bottom of the water. Of these 
are Zannichellia palustris, Ceratophyllum , Vallisneria , and some species of Potamo- 
geton. Among Potamogetons , P. pectinatus is remarkable for wintering by means 
of tubers produced at the ends of special roots. Vallisneria also produces a pseudo 
tuber, which is really a bud at the end of a rootstock. This tuber is eagerly sought 
after by water fowl. A third method of wintering is by means of hibernacula. 
TJtricularia is the best example of this. Toward the fall the tips of the branches, 
instead of elongating, cease growth, and the leaves are crowded into large, compact 
buds. When the plant dies on the advent of cold weather, these buds sink to ne 
bottom, where they remain until spring. The winter buds of certain Potamogetons 
Kolpin Ravn, F. Om Flydoevnen hos Froeneaf vore Vand og Supplanter. Bot. lidsskrilt. vol. 19, pp. 143-177. '76 tig 
