= 
A LYCOPOD _ 
(PEPPERWORT) 
a) 
MARSILEA 
FERN GROWING FROM PROTHALLUS 
BOTANY. 91 
of an Alga or Fungus. In its Protonema stage the Moss 
is only a cellular plant, a Thallophyte. Later, out of the 
Protonema is developed the true Moss, with its stem, 
leaves, and reproductive organs. 
The Mosses have probably descended, through forms like 
the Hypoterygiz, from the Jungermannia. 
EIDICALES. 
The so-called Horse-tails of ditches, etc., our common 
Ferns, the aquatic plants known as Pillwort and Club- 
moss, are generally considered by botanists as representing 
four different orders of the class Filicales. While Ferns, 
etc. are as highly organized as Mosses, in having stems 
and leaves, the vascularity of their stem exhibits a consid- 
erable advance as compared with the same structure in 
Mosses. The Fern and Horse-tail, though differing in 
appearance, are usually associated, since their reproduction 
is the same. The Pillwort and Club-moss, agreeing in 
their reproduction, differ, however, from that observed in 
the Horse-tail and Fern: hence their frequent union. The 
Filicales of the present day play an inferior part as com- 
pared with those of past time. Tropical climates even do 
not give us an idea of what the class once was, as regards 
their size, variety, and importance in the economy of nature. 
They are sometimes called Acrogens, or summit-growers. 
We will examine now a little more closely the living 
Filicales, leaving for the chapter on Geology the account 
of those forms that have died out. 
EQUISETACEA. 
The Horse-tail, or Equisetum (Fig. 121), is a very com- 
mon plant, abounding in ditches, woods, marshes, etc., and 
is readily distinguished by its very characteristic appear- 
