238 RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 



slugs such arrangements are less efficacious. Indeed, these creatures are but little 

 incommoded by adhesive secretions, for they can overcome any obstacles of the kind 

 by themselves secreting a copious slime. Towards spines, prickles and stiff bristles, 

 snails, and indeed all soft-bodied animals are extremely sensitive. Thus whilst ants 

 and the like can travel unimpeded over the rough leaves and prickly heads of 

 Teasels, the soft-bodied organisms avoid hispid and spinose surfaces. Stiff bristles 

 teeth, and prickles, then, situated in the neighbourhood of the flowers, form a good 

 protection against visitors of this class. It should be mentioned that these animals 

 snails and caterpillars do not take especially honey or pollen, but devour indif- 

 ferently the petals, stamens, and carpels. It is hardly necessary to describe these 

 spiny mechanisms in detail here, as the subject has been already treated for the 

 case of foliage (vol. i. p. 433), and the two phenomena have very much in common. 

 Two features, however, may be pointed out as having a direct bearing on the matter 

 in hand; firstly, where flowers as well as foliage are protected by spiny structures 

 against creeping animals, the number of these structures increases markedly in the 

 neighbourhood of the flowers; secondly, it often happens that spines placed imme- 

 diately about the flower serve not only to exclude the unbidden guest, but at the 

 same time as " path-finders " to direct the welcome honey-sucking insect, so that it 

 shall dislodge the pollen and disturb the stigma. 



This latter feature applies in marked degree to the sheathing bract-like invest- 

 ments of many flowers which must be surmounted by insects before they can reach 

 the honey. The small capitate flowers of Composites, Scabiouses, and many Pinks 

 are very rich in honey; but this honey is only for insects which visit the flower 

 from above, where the stamens and stigmas are displayed. The illegitimate removal 

 of honey from below or from the side must be prevented. Now many insects, 

 especially bees and humble-bees, when they come across honey inclosed in a delicate 

 sheath bite through the wall and steal the honey, as it were, through a back-door. 

 Liability to this class of pilfering must be excluded by tough, impenetrable 

 sheathing structures around the basal, honey -containing regions of the flower- 

 Such structures are well shown on the Teasel-heads and capitula of many Pinks, 

 in which the nectariferous portions of the flowers are protected by imbricating 

 scales. The strongest humble-bee cannot pierce them, and the only alternative 

 is to obtain the honey in the legitimate manner. 



It is very generally assumed, and in several cases on adequate grounds, that 

 the inflated calyces and sheaths of bracts which inclose the flowers of many 

 plants serve to protect the honey from marauding of the kind indicated. Thus, 

 in a case in which the honey is distant 20 millimetres from the wall of an 

 inflated calyx, it cannot be reached by the humble-bee whose proboscis is only 

 8 millimetres long by means of a .hole bitten in the calyx. Humble-bees will 

 visit the flower by the ordinary way and get the honey thus with less ex- 

 penditure of energy. But such relations do not generally obtain; in a majority 

 of cases the interval between the inflated calyx, and the honey is less than 

 8 millimetres, so that the average humble-bee could get the honey by biting 



