14 
THE AMERICAN BOTANIST. 
new plants in spring. In the frog-bit (Hydrocharis) the 
runners produce rosettes somewhat after the manner of 
the strawberry, and the plant also forms resting buds in 
autumn. Our common ditch-moss {Elodea canadensis) is 
rapidly propagated by off-shoots and though seldom 
fruiting has become a great pest abroad through its 
rapid multiplication. Indeed, it is said that the pistillate 
plant, onh^, has gone abroad. These extra means of 
propagation seem essential to water plants whose more 
complicated methods of reproduction are often interfered 
with by varying heights of the water. 
The order is represented in both fresh and salt water 
and in both warm and temperate climates. It is notice- 
able, however, that certain families show a preference for 
one or the other of these conditions. Thus the pond- 
weeds are found only in fresh water while the species of 
Ruppia and Zostera are found in salt or brackish w^aters. 
There are about a hundred species of Naiadaceas of which 
nearly three-fourths are pondweeds. The Scheuchzeria- 
ce£e are a small family with less than a dozen species. 
Alismace^e has about seventy -five species, nearly half of 
which belong to Sagittaria. The Vallisneriaceae (known 
also as the H3^drocharitaceae) has about forty species 
man^^ of them tropical. 
THE JAMAICA WALKING FERN. 
(Fadyenia prolifera.) 
Walking ferns, in the sense of ferns whose fronds bend 
over and take root at the tip, are fairly common in the 
fern world. Our owm most noted example is the interest- 
ing little Camptosorus rhizophyllus not uncommon on 
limestone rocks, but we have several others that occa- 
sionally root at the tip, such as the hartstongue (Sco/o- 
pendrium vulgare), the ebony spleenwort {Asplenium 
ebeneum), the pinnatifid spleenwort {A. pinnatifidum) 
and that curious h3^brid named Asplenium ebenoides. 
In the colder parts of the Old World Camptosorus 
sibericus, sl species much like our walking fern, is found, 
but we must turn to the Tropics to find walking ferns in 
