The Structure of Chromosomes

When pollen-mother-cells (or young microspores) of a plant with large chromosomes are mounted in iron-acetocarmine (1), torn chromosomes usually appear to have the consistency of honey or glue, long curling threads extending out from the broken ends. The cytoplasm is more liquid (stage 1). In a day or two, however, the cytoplasm has usually attained the consistency of a firm jelly or of cheese, while the chromosomes are still harder (stage 2). In this state the cell contents may be squeezed flat by carefully graduated pressure, without injury to the chromosomes. In the course of time the hardening progresses, until both cytoplasm and chromosomes become more or less brittle under pressure (stage 3).