178 
INSECTIVOROUS PLANTS 
tonia), Nepenthaceae (Nepenthes), Cephalotaceae (Cepha- 
lotus), and Lentibulariaceae (Pinguicula, Utricularia, Gen- 
lisea, &c.). Of these Drosera, Pinguicula and Utricularia 
occur in Britain. 
They may be divided in groups according to their mode 
of catching their prey. Drosophyllum, Byblis, Roridula, 
Pinguicula, Drosera have glandular hairs secreting a sticky 
fluid to which insects, mistaking it for honey, adhere. In 
the two last named movements of the leaf or tentacles occur 
when stimulated by the presence of proteid bodies. All 
these secrete a digestive fluid which dissolves the greater 
part of the animal substance. Sensitive motile organs, 
which close upon the prey, occur in Dionaea and Aldro- 
vanda, in both of which part of the leaf is modified to form 
the trap. Digestive fluids are secreted in these also. A 
third group is the pitcher plants — Nepenthes, Cephalotus 
and the Sarraceniaceae — in which the leaves or portions of 
them form upright pitchers with hoods over their mouths. 
The upper part of the pitcher secretes honey, which attracts 
flies, and these gradually get further into the pitcher ; the 
inner surface is slippery and they find it more easy to go 
downwards than to return and are ultimately drowned in 
the water at the bottom. It is doubtful whether the plant 
in these cases secretes a digestive ferment, or whether it 
merely absorbs the products of decay and is thus sapro- 
phytic ; the water in the pitcher swarms with bacteria, which 
rapidly decompose organic matter. Lastly there is the 
group of ‘ eel-trap ’ plants — Utricularia, Biovularia, Polypom- 
pholyx and Genlisea — in which animals are caught in traps 
of various shapes, from which there is no escape. They 
decay and the plant absorbs the products. Cf details in 
Pt. II. 
Zones of Vegetation, Plant-Associations, &c. 1 
The local distribution and the periodicity of the climatic 
factors — light, heat, and moisture — are accompanied by a 
corresponding division of the earth’s surface into zones of 
1 Cf. Map of Floral Regions (frontispiece). Drude, Handbuch der 
Pflanzengeographie ; Warming, Oekologische Pflanzengeographie ; Schim- 
per, Pflanzengeographie ; Miall, A Yorkshire Moor , Nature, Aug. 1898; 
Smith, Plant Associations, Nat. Science, 1898 ; and cf. subsequent foot- 
notes. 
