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dium those ferns which differ from Aspidium (or Nephrodiuni)
only in the absence of an indusium, — a character which is often
the result of accident or of arrested development. These species,
nearly one hundred in number, constitute the genus PJiegopieris,
and arc technically distinguished from the true Polypodia by
having the stalks continuous with the rhizoma. The true Polypodia
of the United States and Canadas are but eight in number.
Three of these have the veins free, — P . Plumula, P. vulgare,
and P . falcatum; two — P. Califoniicuni and P. incanum —
have the veins sometimes free, and sometimes sparingly reticulated;
and three — P. Scoulcri, P. aureum, and P. Phyllitidis —
have the veins regularly reticulated, but in three different methods,
representing respectively the sections Goniophhlebium, Phhlebo-
diuin, and Gampyloneurum.
Plate X V I.— Polypodium aureum. The principal drawing represents
a frond collected in Florida many years ago by Mr. S. B. Buckley; but the
coloring is from living plants in Mr. Merrill’s collection. A young plant,
collected by Dr. Edward Palmer, is also figured; and the enlarged drawing
shows the peculiar venation and the position of the sori.
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