12 
THE AMERICAN BOTANIST. 
fished up from the waters of some S'ow stream or pond, 
and offering no characters by which they may be easily 
identified. Nevertheless, these plants are of interest for 
the link they form in the chain of plant famihes and are 
well worth a careful study. 
The Naiadales are named for the genus Naias, or 
Najas as it is often written in the Old World, of which 
the widely distributed Naias Bexilis may be considered 
the t3^pe. The order is also frequently called the Fluvi- 
ales and the Helobiee, but the title we use seems the one 
likely to prevail. Four families compose this group in 
North America and two or three additional families are 
found in other parts of the world. Those represented 
with us are the Naidaceae which includes the pondweeds 
{Potoinogeton)^ the Scheuchzeriacese, the Alismaceae 
containing the water-plantains {Alisma) and the arrow- 
heads (Sagittaria) and the Vallesneriaceae best known 
from the eel-grass {Vallesneria). 
In the simplest plants of this order the flowers consist 
of single stamens and carpels. Sometimes the two are 
borne in the same flower, but often each sex is borne 
alone. These flowers are seen to be much reduced for 
in the group as a whole the regular three -parted type of 
the Monocotyledonous flower prevails. One noticeable 
exception is found, however, in the pondweeds which 
have four-parted flowers. 
As regards the floral envelopes, the flowers of this 
order fare rather better than those of the Pandanales, 
for even in Naias where the flowers consist of single 
stamens and carpels borne separately, the staminate 
flower, at least, not only has a rudimentary sac-like 
perianth but is borne in a spathe as well. In the Scheuch- 
zeriaceas (formerly the Jancaginaceas) there is a sepaloid 
perianth of two whorls of three, while in the Alismaceas 
the flowers have a two whorled perianth, the outer green 
and the inner petal-like and colored. The pondweeds 
have usually been considered as having a perianth of four 
petaloid segments, but these are now regarded as out- 
growths from the anther. While they answer the require- 
ments of petals, they are not petals or sepals in origin. 
