534 
PTERIDOPHYTA 
branched. Sporangia numerous, on ordinary or on meta- 
morphosed leaves, commonly collected into sori. See F. for 
further classification. 
II. Eqaisetineae : Homosporous (some fossil forms are hetero- 
sporous), with dioecious prothalli. Stem much branched with 
jointed internodes and small sheathing whorls of leaves (not 
green). Sporangia on peltate sporangiophores, forming a 
terminal spike. 
[III. Sphenophylleae : fossil plants only.] 
IV. Lycopodineae : Homosporous or heterosporous ; in the latter 
case the female prothallus remains enclosed in the spore till 
fertilisation. Stem simple or branched ; leaves many, small, 
entire. Sporangia singly on upper side of leaf-bases, or in 
their axils, or on a sporangiophore. 
Pteridium Gleditsch = Pteris Linn. 
Pteris Linn. Polypodiaceae. ioo sp. cosmop. P. aquilina L. the 
bracken, is best known, and is common in Brit. It has a creeping 
rhizome, bearing two ranks of leaves. At the base of the leaf is a 
nectary whose use is unknown ; ants may be seen visiting it. The 
sori are confluent along the leaf-margin which is curved over them. 
The bracken is sometimes placed in a genus Pteridium distinct from 
all the other sp. on account of its having a true indusium on the inner 
side of the sorus, in addition to the ‘false’ indusium formed by the 
curving over of the leaf blade. Adventitious buds appear on the 
back of the leaf stalk, near the base (cf. Aspidium). Apogamy occurs 
in P . cretica L. (see Filicineae Leptosporangiatae). 
Pterocarpus Linn. Leguminosae (ill. 8). 20 sp. trop. Several sp., 
esp. P. Marsupium Roxb., furnish Kino, an astringent resin. P. 
santalinus L. f. yields red sandal-wood. The fruit is winged. 
Pterocarya Kunth. Juglandaceae. 4 sp. N. temp. 
Pterocephalus Vaill. = Scabiosa Tourn. 
Pteronia Linn. Compositae (ill). 52 sp. S. Afr. 
Pterostylis R. Br. Orchidaceae (4). 40 sp. Austr., N. Z., New Caled* 
The median sepal, with the petals, forms a hood over the rest of the 
flr. The flap of the labellum hangs out below and is irritable. If 
an insect land on it, it instantly moves up and imprisons the visitor 
against the column ; the only mode of escape is by squeezing past the 
stigma and anther. After half-an-hour the lip goes down again and 
is ready for another capture (Darwin, Orchids , p. 86). 
Ptychosperma Labill. Palmae (iv. 6). 15 sp. Indo-mal. Firs, in 
threes, 2 S and 1 ?. P. ( Seaforthia ) elegans Blume is a favourite 
ornamental palm. 
Pugionium Gaertn. Cruciferae (iv. 18). 2 sp. Mongolia. 
Fulicaria Gaertn. Compositae (iv). 30 sp. Eur., As., Afr. P. dysen - 
terica Gaertn. (Inula dysentcrica L.) in Brit, (flea-bane). 
Pulmonaria (Tourn.) Linn. Boraginaceae (iv. 3). 10 sp. Eur. P \ 
