Yellow Oleander's thick, four-sided, black fruit is really unusual. It's green when immature, then turns a bright, glossy red, and finally it becomes the dull black shown in the picture. Inside is a smooth, brown stone, sometimes called a "lucky nut." Enterprising natives have been known to string lucky nuts on necklaces and sell them as charms to be carried in the pocket.
Above we see that the Yellow Oleander flower is funnel-shaped -- a narrow tube below that flares out above. Atop the narrow basal tube is an area known as the "throat," and in the Yellow Oleander flower the throat is where the flower manages its pollination strategy. Below we look more closely at the "throat," in order to understand the flower's "philosophy" of pollination.
Now imagine that you're a bug drawn into the funnel-shaped flower by its sweet fragrance. When you reach the throat you encounter the star-shaped barrier at the lower right. But the sweet odor attracting you issues from the star's "arms," for those "arms" are nothing but holes blocked with soft hairs pointing inward toward the "arms'" center. You can see that where the hairs meet in the center of each "arm" there's a hole easy enough for a bug to enter, so you do.
In the cross-section at the left the star-shaped barrier you just passed is the fuzzy "roof" at the top of the image, just above the anthers. Once you've passed the barrier, you need to squeeze between the barrier and the stigma head. If you're carrying pollen from another flower, now is when you deposit it on the stigma head, and maybe the pollen grains you've brought will germinate there, send their pollen tubes down through the long style, to the ovules inside the ovary at the flower's base. Once the male sex germ carried by the pollen tube unites with the female sex herm in the ovule, then begins the process of maturing the ovule into a seed, and the ovary into a fruit.
Once you're past the broad stigma head it's easy going the rest of the way down to the nectar, especially since the hairs below the star-shaped barrier all point downward, as clearly shown in the picture. It's clear that once you've deposited your pollen on the stigma, the flower doesn't want you wasting time hanging around the throat; your job is to get down to the nectar, turn around, and leave the flower.
Once you have your nectar and you're leaving the flower, once again the throat area blocks you with all those downward-pointing hairs, this time poking you right in the face. However, in the image at the left, notice the glossy, hairless bulges rising below each anther and between the tufts of downward-pointing hairs. Also note how downward-pointing hairs are absent below the bulges. In other words, you can avoid the downward-pointing hairs by entering one of five hairless "doors, then mounting the hairless mound associated with that entry point.
At the hairless mound's top you're blocked by the bottom of the stigma and have to squeeze between the bulge and the stigma bottom to get out. Notice that the stigma's bottom is notched. These notches invite you to exit in particular places. It happens that the arrangement of hairs, stigma-bottom notches and bulges all oblige you rake past a pollen-coated anther on the way out, and of course that's the second job the flower wants you to do -- to carry its pollen to the stigma head of another blossom, so the whole procedure can be repeated there.
Once you've scraped past the anthers it's just a matter of going through a star-arm hole like the one you entered, then heading to the next blossom.