402 Boodle . — Anatomy of the Schizaeaceae . 
Siliceous Deposits. 
The silica-nodules in Lygodinm dichotomum described above 
are the most conspicuous deposits of silica to be found in the 
Schizaeaceae. They appear to be very similar bodies to those 
described by Poirault (’ 93 ) in epidermal cells of the Marat- 
tiaceae. Besides these, the only other cases of free silica- 
concretions within the cell hitherto recorded among the Ferns 
are those found in the ‘ Deckzellen ’ of Hymenophyllaceae, 
and according to a statement of Mettenius (’ 64 , p. 426), in 
epidermal c Deckzellen 5 of the leaf of Aspidium deltoideum. 
The siliceous bodies in Lygodium agree with those of the 
Marattiaceae, but differ from those of the Hymenophyllaceae 
in haying an indefinite form, and they differ from those of 
both these Orders in occurring in deep-seated tissues, e. g. in 
the stele. 
Among the Angiosperms intracellular silica-concretions are 
found in the xylem-parenchyma and other tissues of Moquilea 
(Kohl, ’ 89 , p. 248), but a closer agreement with Lygodium 
as to the form of the silica- nodules is found in the Podo- 
stemaceae. 
According to Kohl, Ferns are mostly poor in silica (e. g. 
about 5 per cent, of the ash), but Blechnum Spicant and 
Pteris aquilina are cited as having a large amount (about 
53 and 45 per cent, respectively). The silica in these cases is 
possibly an infiltration of the cell-walls of certain specialized 
epidermal cells, as described by Kohl in Antrophyum , &c. 
A few silica-nodules similar to those of Lygodium were 
found in the ground-tissue of Anemia , but none in Schizaea 
or Mohria. 
In Schizaea digitata and in Anemia Phyllitidis the outer 
wall of the epidermis of the petiole has small warts arranged 
in longitudinal rows. Each is due to a refractive, probably 
siliceous body embedded in the wall. They have been 
described by Prantl, and figured by him (’ 81 , p. 33, and 
Taf. 4, Fig. 50), in S. pennula, Sw.,and by Britton and Taylor 
( 01 , PL 6, Fig. 93) in S. pusilla, Pursh. 
