PHYSIOLOGY OF THE FLOWER. Il3 
Pendulous flowers, such as snowdrop, often present an insur- 
mountable barrier in the form of a slippery curved stalk. Re- 
flexed bracts and perianth leaves act in a similar way. We shall 
see (p. 121) that if an insect is to benefit a flower by its visit, it 
must, so to speak, go in by the front door. Bees, even such as 
could get the nectar in a legitimate way, sometimes prefer to bite 
a hole at the side. Certain gamopetalous corollas are frequently 
found neatly drilled in this way. The calyx, epicalyx, and bracts 
often check such a proceeding, either by the toughness of their 
tissue, or, in the last case, by crowding. It also seems likely that 
an inflated calyx, like that of the bladder-campion, is a special 
arrangement for protecting the nectar. Parts of the flower are 
often so arranged or shaped as to entirely or partly block up the 
way to the nectar (which lies deep down in the blossom), in such 
a manner that small insects are unable to get at it. Very strik- 
ing examples are afforded by the personate corollas, e.g., that of 
snapdragon. Only humble-bees are sufficiently heavy and strong 
to force down the lower lip of this flower. Stamens may also 
form obstacles. In heath the large anthers serve this end; in 
harebell and Canterbury bell, the dilated bases of the filaments. 
Cinquefoil secretes nectar on the inner side of the concave recep- 
tacle, and the numerous perigynous stamens slant upwards and 
inwards, thus forming a roof forit. Narrow or constricted corolla 
tubes—knobs, ridges, or swellings in the perianth—nectar-con- 
taining spurs—crowded petals, stamens, and carpels, all these 
frequently have to do with the protection of nectar from unbidden 
guests. Still other devices are found. 
(g.) Wingless insects are most active when the dew has evapo- 
rated, and this is a signal for the closing of many flowers. 
(h.) Some forms again secrete substances in parts away from 
the flower, which serve to divert the attention of unwelcome 
insects. Beans and vetches, for instance, possess ‘‘ extra-floral ”’ 
nectaries on the stipules, while common laurel, almond, and peach 
develop them at the base of the leaf-stalk. 
Equally varied are the means of protection against wet and wind. 
(a.) Many flowers close in unfavourable weather. (0.) Parts of 
the perianth often form a kind of roof or penthouse which covers 
over the internal organs, and the efficiency of which is often 
enhanced by a covering of hairs. Good examples are seen in the 
hairy calyx and forwardly directed standard (p. 88) of gorse, 
and the arched upper lip of the dead nettle. The spathe of arum 
protects an entire inflorescence (fig. 33). Rain will obviously 
run olf the outside of pendulous flowers, such as harebell and 
snowdrop, without doing them much injury. (c.) Nectar, again, 
is so slippery in nature, that rain can only with difficulty wash 
H 
