IOWA ACADEMY OP SCIENCE 
131 
NOTES ON HETERANTHERA DUBIA. 
BY KOBEET B. WYLIE. 
. One of the common acquatic plants of our Icwa lakes is Heteranthera duMa 
(Jacq.) MacM. In the lakes of the Okohoji region this form is conspicuous 
along sheltered shores of suitable depth. While only sparingly present on the 
more exposed margins of the larger bodies of water it grows luxuriantly in the 
shallower bays and associated smaller lakes. In waters of appropriate depth 
considerable areas are often dominated by this form, sometimes to the ex- 
clusion of other large plants. During the summer of 1910 many acres of the 
“long slough” south of Center Lake were occupied almost exclusively by this 
species. Portions of the upper end of East Okoboji Lake were occupied this 
past summer by extensive beds of this plant where for a number of years it 
had developed but scantily owing to the higher water level. The writer desires 
in this brief article to call attention to the apparently uniform cleistogamy of 
this plant in such habitats. 
In common with other submerged seed-plants that have not developed the 
habit of pollination beneath the surface of the water this species of Heteranthera 
is forced to bring its flowers to the air if cross-pollination is to be. affected. In 
favorable habitats the plants may be two or three feet in length and stand 
nearly erect buoyed up by the water. Under such conditions the plants may 
never reach the surface of the water even at the end of the growing season. 
If in shallower water the plants are turned at the tip and lie horizontal near 
the surface of the water. In this relation the younger portions of the plant 
which bear the scattered flowers would, be in most favorably placed with 
reference to bringing the flowers to the surface. The plants thrive best however 
under conditions that permit few, if any, of the flowers to open at the surface 
of the water. 
The flowers are perfect and the tubular perianth is surrounded by a spathe 
which completely invests the developing blossom. The stigmas, etc., are 
brought to the air, if at all, by the elongation of the flower, which is sessile 
and hypogynous. Since the maximum elongation of the slender flower is but 
three or four centimetres it follows that a plant must be most favorably placed 
if the flowers open above the water. 
The open perianth displays a six parted limb with its slender segments 
nearly symmetrically arranged, and this has no doubt suggested the common 
name “water star grass.” Within the slender flower are the three stamens, 
which are not radially disposed and give to the blossom a zygomorphic ap- 
pearance. The style is long and very slender and bears at its tip a fringe of 
large glandular hairs. Within are the chambers through which the pollen- 
tubes make their way to the ovules. 
This floral structure, while well adapted to quiet waters of limited depth, 
seems illy fitted to the average habit of the plant. Owing to the limited length 
of the flower it can reach the surface only under restricted conditions and 
those not the most favorable for vegetative growth. The writer has studied 
