TAKING UP OF POLLEN BY INSECTS. 251 



after the interior of the flower becomes accessible, owing to the opening of these 

 sepals, the anthers belonging to the outermost whorl of stamens dehisce. Their 

 filiform filaments have in the meantime undergone elongation, inflection, and torsion 

 to the extent necessary to bring the anthers exactly over the opening admitting 

 to the little cups full of honey. Insects cannot suck the honey without brushing 

 against these anthers. The next day the stamens of the first whorl move in an 

 outward direction towards the sepals, their place being at once taken by the stamens 

 of the next whorl nearer the centre of the flower. By the third day these, too, are 

 reflexed and replaced by the members of the third whorl; and the process continues 

 until all the stamens in turn have set their anthers over the nectaries. The 

 punctuality and exactitude with which the whole series of operations is carried out 

 is most extraordinary. 



The same phenomenon may be observed in the flowers of the Grass of Par- 

 nassus {Parnassia palustris). Only here the number of stamens is limited to five, 

 and one anther at a time is set in the way of alighting insects as is shown in 

 fig. 267 *- The honey is secreted in two small oblong depressions on the inner face 

 of certain curious flmbriate leaf -structures which are inserted between petals and 

 stamens (267 ^). If an insect in search of honey alights from above on the middle 

 of the flower, it is certain to brush its proboscis against the particular anther which 

 has set free its pollen that very day, and is itself in close proximity to the approach 

 to the honey. The Grass of Parnassus possesses in addition another extremely 

 interesting contrivance correlated with the movements of those insects, which, 

 instead of alighting from above, settle on the edges of the petals. When such an 

 insect moves from the margin of the expanded petals towards the nectaries it 

 encounters a barrier in the form of railings composed of the radiating arms of the 

 nectariferous scales. This barrier is not, however, insurmountable; its radiating 

 arms do not secrete any viscid substance or terminate in sharp points, but are 

 surmounted by round yellow knobs, resembling pins' heads (see fig. 267 ^). The 

 insect easily climbs over this obstacle without hurting itself, and then finds itself 

 on the side of the scale where the nectaries are. But in doing so, it is brought so 

 nearly to the middle of the flower that it is sure to touch the anther, which, having 

 opened that very day, occupies the position commanding the passage to the nectar. 

 We have here an instance of the adaptation of a flower to different visitors. Both 

 those which settle from above and those which crawl from the edges of the petals 

 are obliged to brush against the eflfective anther in the middle of the flower and 

 besmear themselves with its pollen. 



In all these cases the pollen pours in copious quantities from the anthers and 

 forms either puffy masses which cling to the gaping loculi, or else a viscid mantle 

 clothing the slender style, when that organ has been used to sweep it out of a tube 

 of syngenesious anthers. Insects, on visiting the flowers, come into immediate 

 contact with the pollen, it being in no way covered or wrapped up, and being 

 obtruded so directly in the path that to avoid it would be impossible. In the next 

 series of plants there is a certain amount of difference in this respect. The pollen 



