Egeria (plant) Egeria (plant) Egeria is a genus of three species of aquatic plants in the family Hydrocharitaceae described as a genus in 1849. native to warm-temperate South America. The genus was formerly included in the related genus "Elodea", from which it differs in having the leaves in whorls of four or more, not three, and in having more conspicuous flowers with larger (particularly broader) petals. "Egeria" is found in many temperate and subtropical regions throughout the world as an introduced, or "alien", species, meaning a species that does not originate from the area in which it is found. In many places,
How many angels can dance on the head of a pin? about how many could perch at the same time on the head of a pin"". Dorothy L. Sayers argued that the question was "simply a debating exercise" and that the answer "usually adjudged correct" was stated as, "Angels are pure intelligences, not material, but limited, so that they have location in space, but not extension." Sayers compares the question to that of how many people's thoughts can be concentrated upon a particular pin at the same time. She concludes that infinitely many angels can be located on the head of a pin, since they do not occupy any space there: