It was while I was wrestling with that problem, and evaluating alternatives! — none of them satisfactory — that I was approached by a scientist, Livia Morgan. She offered an intriguing prospect. She could, she claimed, develop symbiotic forms that combined organic and inorganic components. By the end of our first meeting, I was convinced that what she had might be perfect for our needs.” Mondrian nodded at one or the figures in front of him. “I also knew of at least one example, sufficient to prove that such a blend of organic with inorganic was not impossible.”

The Angel acknowledged the reference with a wave of blue-green fronds. It was itself a symbiotic life-form, discovered a century and a half earlier when the expanding wave-front of the Perimeter had reached the star Capella and the planets around it. The visible part of the Angel was the Chassel-Rose, slow-moving, mindless, and wholly vegetable. Shielded within the bulbous central section lived the sentient crystalline Singer, relying upon the Chassel-Rose for habitat, transportation, and communication with the external world.

“Imitation is the sincerest form of flattery,” said the computerized voice of the Angel.

Mondrian stared back at the gently waving fronds. The Angels had that disconcerting habit of employing human clichйs and proverbs at every opportunity. No one was ever sure if it represented the symbiote’s perverse ideas of racial politeness, or served some wild sense of humor.

“Regarding the entities that Livia Morgan proposed to create.” Mondrian had realized after a few seconds that the Angel intended to offer no further comment. “I will from this point term them the Morgan Constructs. They were designed specifically to patrol the Perimeter. Their performance specifications were drawn very precisely. Each unit had to be mobile, durable, and highly intelligent. Livia Morgan told me once that they would be — I quote — ‘indestructible.’ Fortunately, she was exaggerating.