POLLINIZERS 



Pitcherplants, by their trap structure almost unique in their relations to the insect world, 

 do not confine those relationships to the status of trap and victim. The flowers of Sarracenia 

 are dependent upon insects for their pollination, and they are adjusted structurally and phys- 

 iologically to encourage, if not to enforce, cross-fertilization by insect agency. 



For example, the globular flowerbud of Sarracenia flavaj in March or April, pushing up 

 rapidly from its fleshy rootstock, is at first held upright upon its stem; but before the swell- 

 ing bud has lost its globular form, it makes a complete reversal of position, so that when 

 the petals expand the flower opens downward. The promptly shed pollen falls into the 

 concavity of the umbrella-shaped style which closes the flower below. The stigmatic points 

 are entirely outside the dome-shaped cavity formed by the petals and having the style as 

 its floor; for they are located, one at each of the five projecting points of the umbrella. A 

 visiting insect, alighting on the shelflike base of a petal, turns either right or left to an open- 

 ing between two adjacent petals and under one of these points, against which (if the insect 

 should be of suitable size) it scrapes its pollen -dusted back as it enters. On departure, the 

 insect may leave the flower by the same route; but especially in the more loosely textured 

 flowers of other species, escape is readily and more frequently made at some other point 

 around the edge of the umbrella. 



Though the pollen is shed promptly after the opening of the flower, nectar continues 

 to be secreted and insects attracted for many days, even for several weeks, after that event; 

 and a further change in the position of the flower (this time toward the vertical) commences 

 within a day or two of its opening, thus tending to spill out the pollen and to permit visiting 

 insects to avoid intimate contact with that which may have accumulated in the concavity of 

 the style. These phenomena bear out the interpretation that in Sarracenia the fall of the pollen 

 is antecedent to the receptivity of the stigmas of an individual flower, and that fertilization 

 is effected by an entering insect which has received its pollen-coating in another flower. 



Ants, bees, and pollen-eating beetles are aU frequent visitors to the flowers of Sarracenia. 

 Among their visitors, thick-bodied bumblebees can scarcely force an entrance between the 

 petals without scraping one of the stigmatic points; the Sarracenia flies frequently crowd into 

 the blossoms, apparently more for shelter at night and in bad weather than in search of food; 

 honeybees are regular visitors, and they more nearly fit the entrances than do the smaller wild 

 bees of several species, which, nevertheless, are usually the more numerous among the insect 

 visitors and which are probably the insects most concerned in effecting fertflization. Thus 

 these flowers, attractive to a considerable range of insect species, are not dependent upon any 

 one insect for the transference of their pollen from flower to flower. 



PLANT-EATING INSECTS 

 The most familiar plant-insect relation is that existing between a foodplant and the insect 

 which attacks it. Several insect species have the Sarracenias as their preferred or their sole food. 



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