100 INTRODUCTION 
their wings and keel, the Labiatae and Scrophulariaceae in their lower lip, and similarly 
in Orchids, many Ranunculaceae, and so on (cf. Fig. 16). The special arrangements 
of this kind will be dealt with in the second part of this work in connection with the 
description of particular floral adaptations. The alighting place is always so situated 
that insects suitable for the work of pollination touch either the pollen-covered 
anthers or the receptive stigma. On the other hand, such insects as are not able to 
effect pollination, and are therefore useless or even in many cases injurious to the 
plant, are kept away from the flower by very varied contrivances. Kerner, who has 
described such insects as Unbidden Guests, distinguishes the following Protective 
Arrangements (‘ Nat. Hist. Pl.,’ Eng. Ed. 1, II, pp. 231-43) :— 
1. Against wingless animals that creep up from the ground, 
(a) The nectar of extra-floral nectaries keeps ants away from the flowers—as 
these insects make use of the honey thus found on the way up, and do not trouble 
to go to the flowers: Impatiens tricornis. 
(4) Isolation of the plants by water. Owing to the habitat of the plants being 
in water, their flowers are only accessible to flying insects; the blossoms of all marsh- 
and water-plant’ are thus protected against creeping animals. The water collecting 
in the leaf-sheaths of Dipsacus and Silphium perfoliatum, and in the funnel-shaped 
sheaths of the leaf-rosettes in many Bromeliaceae (Aechmea, Tillandsia, Billbergia, 
Lamprococcus), serves the same purpose. 
(c) Access to the flowers prevented by sticky material, occurring either as rings 
or streaks on the stem (e.g. in Silene Otites, Viscaria vulgaris), or else in the 
form of adhesive glands or glandular hairs on the peduncles and calyces (e.g. 
Ribes Grossularia, Epimedium alpinum, Circaea alpina), or on the foliage leaves 
(Pinguicula vulgaris and species of Drosera, in which the visitors are afterwards 
digested by the leaves). 
(d) Hindrance by wax-like coatings on the peduncles and twigs. The slipperiness 
thus produced interferes with access to the flowers, e.g. in Salix daphnoides and 
S. pruinosa. 
(e) Sharp thorns, prickles, or stiff bristles on stems, leaves, or inflorescences prevent 
soft-skinned creeping animals, especially snails and slugs, from climbing up to the 
flowers (Ulex, Rubus, Eryngium, and many others). 
2. Against unbidden guests which can fly. 
(a) By the development of hairs and bristles inside the flower, which either com- 
pletely fill it, or only make up a hirsute circlet or tuft above the nectary. Weels 
and gratings are thus constituted, which prevent small unbidden guests from entering 
the flower, while an invited one is able to thrust its proboscis between the bristles 
(Veronica officinalis, Lonicera alpigena, Menyanthes trifoliata, and others). 
(6) By the development of special floral arrangements, which can only be opened 
by insects that are specially adapted for the work of pollination, as in numerous 
Papilionaceae, Labiatae, Scrophulariaceae, Corydalis cava, and others. 
(c) By an inflated vesicular calyx, which serves to protect the flowers, especially 
against honey-stealing humble-bees. There are two humble-bees in particular which 
in consequence of the shortness of their proboscis are not able to reach in the usual 
