232 RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 



cushions, walls and gratings, brushes and thickets of hairs are present, guai-ding 

 the entrance and rendering access diiBcult, whilst still allowinor it. Laree and 

 powerful animals find these obstacles no hindrance, and readily brush them aside; 

 small ones, however, cannot do this, but have to climb over or circumvent the 

 obstacles. And in many cases this enforced divergence by small insects from the 

 direct path brings about the desired result. For, in circumventing these folds and 

 barricades and hairs, they are unconsciously led past the anthers and stigmas, 

 contact with which is unavoidable. Thus, what would otherwise be useless visitants 

 become welcome guests. They are conducted indirectly to the honey by these 

 curious structures, which may, in a sense, be termed " path-finders ". 



A more detailed consideration of these arrangements will be given when treating 

 of the taking up of pollen by insects, in the next chapter. Mention of them cannot 

 be omitted hei-e owing to the difiiculty of drawing an absolute distinction between 

 contrivances designed to lead insects by a particular route into the flower, and such 

 as entirely exclude the unbidden guests. The same difficulty obtains between the 

 defences erected against wingless and those against winged insects, it being in many 

 cases not easy to distinguish between them. Consequently, the grouping of these 

 mechanisms in the sequel cannot be entirely free fi-om the reproach of partiality; 

 still it will serve its purpose should it render these problems more intelligible. 



First of all, we will describe the mechanisms which serve to protect flowers 

 against little wingless marauders which creep up from the ground. Remarkable 

 amongst these is the indirect protection afforded to the floral honey by honey 

 secreted in the region of the foliage. This may be seen in many Balsams, especially 

 well in the Himalayan Impatiens tricornis. In this plant the stipules, which stand 

 right and left at the bases of the leaves, are modified into secretory glands. Of the 

 two glands, one is small and rudimentary, but the other extremely well-developed. 

 The latter is a fleshy convex disc fused partly with the base of the leaf and partly 

 with the surface of the stem, and so disposed that insects creeping up the stem must 

 encounter it. The honey, secreted by the tissue of this gland, collects in a drop on 

 the hemispherical and downwardly-directed cushion of this disc. Thus are the insects 

 tempted by the way in their ascent. They find drops of honey provided for them 

 at the base of every foliage-leaf equalling that of the flowers in quality and sur- 

 passing it in quantity; besides which it is nearer and more accessible. The honey- 

 loving ants lick it up eagerly, and are content not to stray further upwards. Actual 

 observation shows that the flowers of Inipatiens tricornis are free from ants, whilst 

 these stipular nectaries are much frequented by them. Their presence in the flowers 

 is very undesirable, since they could readily get at the honey thei-e without touching 

 the pollen or stigma. And more than this; they would not only pilfer the honey, but 

 they would also drive away those wingeil insects for which the honey is prepared — 

 the welcome guests that pollinate the flowers. We are justified on the facts in 

 regarding this diversion of the unbidden guests as an indirect protection of the floral 

 honey. 



This secretion of honey from the stijjules in Irnpatiens tricornis begins just at 



