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In Aconitum columbianum there are extreme interpopulation differences in rates of nectar secretion per flower. Since nectar sugar concentration varies little among populations, increased nectar secretion results in a greater mass of sugar per flower for pollinator attraction. These differences in the amount of reward offered per flower account at least in part for observed higher levels of pollinator activity in populations with high nectar production. Nectar production is correlated also with nectary depth, i.e., flowers in populations with deep nectaries have higher rates of nectar secretion than those with shallow nectaries. Nectary depth differences adapt populations to different pollinator-types. Populations with deeper nectaries are adapted to pollination by bumblebees with longer tongues and more specialized foraging behaviors. In conclusion, there are basic differences in pollination ecology among geographical races of a. columbianum, which are indicated by correlated interpopulution differences in (1) nectar production, (2) level of pollinator activity, (3) nectar depth, and (4) pollinator-type.

Our study of caudatum sorghums in Africa and the ethnography, history, and archaeology of regions where caudatum sorghums are grown has led us to the following conclusions.The distributions of caudatum sorghums and Chari-Nile-speaking peoples coincide so closely that a causal relationship seems probable.Caudatum sorghums appear to be a product of selection by Chari-Nile-speaking peoples for a hardy crop which will produce a large amount of grain under adverse conditions with a minimum amount of care. Caudatums can produce grain in spite of either droughts or heavy rains during the growing season and can produce grain in places where no other indigenous African crop can grow.Caudatum may be a relatively new race of sorghum. Available evidence indicates it was developed some time after about 350 A.D. and before about 900 A.D., the date for caudatum found at Daima mound, south of Lake Chad.By about 1000 A.D. caudatum was probably being grown in many parts of the savanna belt stretching from the eastern shores of Lake Chad to southwestern Ethiopia. This is assuming that the evidence of caudatum culture at Daima is indicative of a general phenomenon occurring in a region with close intercultural contacts.The large number of varieties of caudatum in the Republic of the Sudan suggests that caudatum sorghums have been grown in the Sudan for a relatively long time and may have been developed there.A caudatum and cattle-based economy has probably been an important factor in making possible the present level of occupation of regions now inhabited by Chari-Nile-speaking peoples.On the basis of oral histories and archaeological remains of people in northern East Africa, we have concluded that caudatum-based agriculture was probably introduced to Uganda and Kenya no later than the period from 1500–1800 A.D., when the Luo occupied the areas in which they live at the present. However, it is not unlikely that caudatums were introduced more than once as various Chari-Nile-speaking groups made their way into East Africa.