
AQUATIC PLANTS OF FRESHWATER 

the epidermal cells of the foliage leaves and not by roots, though the lower 
leaves may assume a rootlike character. The Hornworts have weak and 
slender widely-branching and floating stems with verticulate leaves, which 
appear in thick clusters on the younger growth and branches. It is not a 
desirable aquarium plant as it is too fragile and requires careful attention, 
may decay in a brief period, contaminate the water, and cause the death 
of the fishes. Several species have been proposed, based on the spurs, 
spines or wings of the fruit but none of these distinctions are of value. 
Ceratophyllum demersum (Gray), or Common Hornwort, Fig. 125, 
has long or short slender submerged floating stems, dependent upon the 
depth of the water, as it is characteristic of the plant to form thick mats 
immediately below the surface. The linear 
2 to 3 times divided and forked leaves grow : \\ 
in verticils of 5’s to 12’s on a weak and aM " 
fragile stem. The flowers are insignificant, h ve \ mi 
either white or yellowish in color,of which the wl 7 Is us ; a 
AY 
ye wily mt we 

male and female are distinct. The former 
consists of about 15 sessile anthers and the 
latter of a small one-seeded ovary, but both 
surrounded by a whorl of very small bracts, 
while the fruit is oval with either a straight 
and spinelike beak, smooth or with a basal 
spur, or tubercular with narrow winglike spiny 
lower margin. Grows freely 1n ponds and 
slow streams throughout North America 
except in the extreme North. European 
NRE 
oa . : pes, Ss 
VAN SS 
authoritie nti wo r : , 
uthorities mention t other species, C WG 
submersum and C. platyacanthum, not gener- ANA 
ally known in the United States. They are ERY 
probably natural variants of C. demursum the TK WT 
. . . . eA VA 
universally distributed species. SZ 
F Z Wi SWF 
Podostemon ceratophyllum (Linn.) 1s ) \ Sy 
‘ x NY OZ, 
another aquatic bearing the name Cerato- SINS WZ 
. - a7 aS yy 7 
phyllum. It is popularly known as River Hf SK 
Weed or Threadfoot, and is a dark green 
rather stiff plant, firmly attached to the praelene an ene 
stones in funning streams, The densely, 8= = Se 
tufted leaves are narrowly linear and sheathed at the base, but split above 
into filiform segments. It resembles C. demersum but is coarser and 
rougher in appearance. The white flowers are 34 to % inch broad, 
spreading from the spathes; and the oblong-oval capsules are borne ona 
198 
