The development of the pattern of growth.

It is proposed that the varying patterns of growth in development can be viewed as an aspect of pattern formation, and that different growth programmes are specified at an early stage. This is illustrated largely with respect to the development and growth of the chick wing. The spatial pattern of cellular differentiation and programme for growth can be considered in terms of the concept of positional information. The lengths of the cartilaginous elements are determined by the initial length of the primordium and its later growth, involving cell multiplication enlagement and matrix secretion. It seems that tissues have a high degree of autonomy with respect to differentiation and growth after they have had their position specified. The cellular basis of programmed growth is discussed.