Mid-August and the berry crops of wild currants are ripe. The stink currant (reportedly so-called for the smell of crushed leaves) sometimes bears large crops of berries, which are conspicuous for the white “bloom” that covers each black berry.

Other local species of currant produce black berries that lack this bloom, although one species is said to have a waxy bloom, no color given. Other local species also make berries that have a bloom, including most blueberries (but not the Alaska blueberry), serviceberries, and junipers. (And crowberry, black berries with NO bloom.)

So far, I have not found any red-fruited species that have a bloom on the fruit — except native mountain ash fruits may have a hint of a bloom. Those observations stir up questions! Why more commonly on blue or black-fruited species, and why just some of those? And why is this feature called by a name that otherwise refers to flowers?

What might be the function of the bloom? It is produced by the plant and is reported to reduce water loss from the fruit and perhaps protect against insects and pathogens or solar radiation, but so far I have not found any direct evidence of this.

Another kind of fruit is conspicuous at this time of year — the red elderberry. This shrub is native to Eurasia and North America. In most populations the berries are indeed red, but in certain places they are black-purple. Almost all parts of these plants are said to be toxic, including the seeds. But the flesh of the berries may be edible and at least perhaps flavorful. Confusingly, although some reports say the berries are edible, many reports say that the fruits are toxic, containing cyanogenic glycosides, but cooking may reduce the toxicity. Perhaps the level of toxicity in the fruit pulp is quite low or variable? Birds and bears often eat the fruits and disperse the seeds, and some Native groups have also done so (presumably excreting the seeds, as the other consumers do). How do bears and bird manage the toxicity?

Baneberrry plants are bearing showy fruit clusters — usually red, but occasionally white. The fruits are reported to be very toxic to humans (what about bears?). However, birds readily eat those fruits, apparently not finding them toxic, and disperse the seeds. How do birds tolerate the toxins or detoxify those fruits?

Devil’s club also produces bright red fruits in showy clusters. The fruits are eaten by birds and bears, but they are not considered to be edible for humans. Again, one must ask, what is missing in human chemistry that makes these fruits inedible, although other vertebrates consume them happily.

• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.