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PTERIDOPHYTES (FERN PLANTS) 
The character of the sporangia and the way they are borne vary 
much in different Ferns and are much used in the classification of 
Fic. 381.— A sporophyte and spore- 
producing structures of a True Fern. A, 
a Fern sporophyte, showing roots (7), 
stem (st), and a leaf (/) (x about 3). B, 
an enlarged view of the under surface of 
a Fern leaf, bearing sori (so). C, highly 
magnified section through a Fern leaf 
and sorus, with section of leaf shown at 
1, sporangia at sp, and indusium ati. D, 
a much enlarged view of a sporangium, 
showing annulus a and method of opening 
to allow the spores (s) to escape. 
Ferns. In the lowest group 
of the True Ferns the spor- 
angia are borne in syn- 
angia, which are apparently 
composed of united spor- 
angia. In some Ferns the 
sporangia are borne singly. 
In some the sori have no 
true indusium, but the edge 
of the leaf folds over and 
protects the sporangia. 
Then in the shape of the 
sporangia, presence or ab- 
sence of an annulus, the 
location of the annulus, 
and in the number of 
spores borne in a sporan- 
gium, there are important 
differences among Ferns. 
Again there are two ways 
in which sporangia begin 
their development. In 
some Ferns, known as 
eusporangiates, both epi- 
dermal and sub-epidermal 
cells of the leaf are involved 
in forming the sporangia, 
while in- Ferns, known as 
leptosporangrates, the spor- 
angia are formed entirely 
from the epidermal cells of 
the leaf. 
In some of the True 
Ferns the sporangia are not 
borne on ordinary leaves, 
in. which case the sporo- 
phyte is differentiated into vegetative and spore-bearing regions. 
Sometimes some of the leaflets are devoted entirely to bearing 
