The Aceto-Carmine Method for Fruit Material

It is not easy to make good aceto-carmine preparations of plants with small chromosomes at meiosis because the cytoplasm readily takes up the stain and this prevents a sharp differentiation. The staining reaction depends on the composition of the pre-fixative, the duration of fixation, strength of aceto-carmine and amount of iron used. These factors can be varied independently. Since not only species but their varieties differ markedly from one another in their behavior, the best results can be secured only after experiment with individual plants to discover the most suitable combination. Suitable combinations of these factors for some fruit plants are described. In general they demand (1) a weaker solution of aceto-carmine and more iron than has hitherto been used in the aceto-carmine technic, and (2) the introduction of iron and carmine into the pre-fixative. Iron acetate is added to a dilute solution of carmine in glacial acetic acid until the solution assumes a deep red color, without precipitation, and this solution is used as the acetic acid component of an acetic-alcohol pre-fixative. Anthers are colored purple by treatment with this fixative, but since it has only a mordanting effect they need to be smeared and stained in the ordinary way.