ABSTRACT
The mode of action of genes during development can be investigated in two ways: (1) by experiments on the mechanism of development, (2) by examination of the changes produced in developing organisms by gene-changes. The first field of inquiry is usually considered to constitute the separate science of experimental embryology, while the second is a part of genetics, and is often referred to as phaenogenetics. Such a separation is, however, very artificial; both subjects fall into the general field of investigation of how an adult organism arises from the individuals of the previous generation. Thus some at least of the results of experimental embryology are essential for a full understanding of genetics, and in this chapter we shall consider the general mechanism of the development of animals and the ways in which genes may act to control the course of the reactions involved. Unfortunately there are no adequate data for a similar survey of genetic control of plant development.
