Hugo de Vries

The Present Position of the Mutation Theory

DARWIN assumed that species originate by the gradual accumulation of infinitesimal, ordinarily invisible variations on account of their utility in the struggle for life. The difficulties inherent in this conception have led to the theory of mutation, which supposes that the production of species and varieties proceeds by small but distinct steps, each step corresponding to one or more unit-characters. It is only after their appearance that the environment can decide about their utility.

How to make Colourless Specimens of Plants to be preserved in Alcohol

MANY plants assume a brown colour when placed in alcohol for preservation. The colouring-matter is partly soluble in the alcohol, partly not, and is the product of the oxidation of colourless substances of the cell-sap. This unpleasant change may be prevented in a very easy manner by using acid alcohol. To 100 parts of common strong alcohol add 2 parts of the ordinary concentrated solution of hydrochloric acid of the shops. Parts of plants brought into this liquid while yet living will become absolutely colourless, or nearly so, after the alcohol has been sufficiently often renewed. Such parts as already had a brown colour before, being brought into the mixture, usually retain this character.