In a number of trees branches were derived of all buds save one. The main characteristics which distinguished the shoots developed from the remaining bud, when compared with the control shoots, are the following: (1) they are longer; (2) their development stops much later in season; (3) they develop a greater number of leaves; (4) the leaves are considerably larger. Branches which were cut from the trees showed more or less the same phenomena, but the leaves in most cases did not reach their full size. The abnormally large dimensions of the test leaves were attained by cell division (with one exception) when the branches were left ■on the trees; on cut off branches most species examined achieved the correlative enlargement by cell stretching. Leaves of a number of herbaceous plants also attained abnormally large dimensions, when the top and the axillary buds were removed; in these species the enlargement was due to cell stretching. It is pointed out that the capacity of cell division in leaf blades is more widely spread than is generally accepted. The expansion of leaves can be achieved by cell multiplication and by cell stretching. The part which each of them take in this growth process can vary according to the species, according to the different parts of a leaf, according to the different tissues, according to the many possible external conditions. I want to express my heartfelt thanks to everyone in the Botanical Institute, the National Herbarium and the Botanic Garden at Leyden who helped me to carry out these researches. I have also great pleasure in thanking mr. J. Kalsbeek, certified horticalturist from the Government Horticultural College at Boskoop for his valuable help in many respects.