[Development of leaf-form in Antirrhinum majus L. and some mutants]

1. Length and width of the leaves from 2 normal types and 10 mutants of Antirrhinum majus ("races") were measured at different stages of development. 2. The two opposite leaves have nearly the same size and form. 3. The values for length, width, form, speed of growth and duration of the growth phase were different according to the position of the leaf and the race. 4. Length, speed of growth and duration of the growth phase show first an increase with the position number of the leaf and then a decrease towards the higher position numbers. 5. The maxima for the values of these various properties do not fall on the same position number. 6. The single leaf changes its form during the development. This change depends on race and position of the leaf. The length/width-index can increase or be constant; in no case was a decrease found. 7. The position of the broadest part of the leaf in relation to the total length varies according to race and position number and is independent of length and width of the leaf. 8. The form of the leaves and the changes of form during the growth in general are not typical for a race. Characteristic are the direction and the extent of the changes in form during the growth of the leaves in the different positions on the stem. 9. The growth lines (length/time) of leaves in the same position on the plants of a race are parallel. 10. The development lines (length/width on a double logarithmic scale) which describe the relation of growth in length and width are parallel for leaves of the same position and race. The relation of growth in length and width is independent of the width of the leaf at the beginning of the phase of development which was measured. 11. At the end of the phase of allometric growth a growth in only one direction can occur. 12. The following parameters determine the development of the leaf form: width at the beginning of growth in length, regression of the developmental line, length of this line and the occurrence of an end phase with growth in only one direction. 13. The time during which growth occurs is of no importance for the development of the form of the leaves.