Jewelweed (Impatiens pallida), also known as Touch-Me-Not due to the sensitivity of its bursting seed pods, illustrates a strategy used by many flowers to promote cross-pollination. The male and female parts of the flower develop sequentially — first the male (stamen), then the female (pistil), so that they are not mature and receptive at the same time. The bumblebee in this photograph is squeezing into the spur of a Jewelweed flower in order to reach the sweet nectar it contains. In doing so, its back brushes against the strategically located, pollen-laden anther (tip of male stamen). When the bee enters another Jewelweed flower, if its pistil is mature, some of this pollen is likely to brush against the stigma (sticky tip of the female pistil), thereby cross-pollinating the flower.
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A commonly held belief is that in order to be cross-pollinated, flowers have evolved to attract certain pollinators, including wind, mammals, birds and insects. These traits, or “pollination syndromes,” include the flower shape, color, odor, amount of nectar and flowering time. Flowers attractive to hummingbirds tend to be large, tubular-shaped and colored red, orange (or sometimes yellow). These flowers usually have a large supply of dilute nectar, which they secrete during the day. Since birds do not have a strong response to scent, the flowers they visit tend to be odorless.
Canada Lilies, found throughout eastern North America, have a distinct tubular shape, which appeals to Ruby-throated Hummingbirds. Their long, thin beak allows these birds to reach nectar at the base of the flower that is inaccessible to many other creatures. In order to reach the nectar, the hummingbird must enter the flower far enough so that its neck and breast press up against the orange pollen-laden anthers of the Canada Lily. When the hummingbird moves on to the next Canada Lily flower, it is very likely that some of this pollen will end up on the flower’s female structure, or stigma, thereby pollinating the flower. (Note that the stigma, in the center of the flower, is taller than the anthers, thereby discouraging self-pollination.)