The effect of prefixation on the diameter of chromosome fibers isolated by the Langmuir trough-critical point method has been investigated in several species of plants and animals. In barley, fibers isolated from endosperm without prefixation have an average diameter of between 240 and 250 A, and are similar in dimensions and structure to the chromosome fibers isolated from animals by this method. Chromosome fibers from other tissues of the same plant are smaller in diameter when isolated without prefixation, approximating 200 A. After prefixation in 2% buffered formalin, isolated fibers from the three barley tissues studied are reduced in diameter, to approximately 120–130 A for endosperm and leaflet and to 140 A for root tip. Chromosome fibers isolated from newt erythrocytes also show a significantly reduced diameter after formalin prefixation, to approximately 120 A.

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