Dimorphism has been noted to occur in the branches of various plant genera such as Gossypium, Theobroma, Hedera, Musa, Araucária, Castilla and also in Coffea. This phenomenon is characterised by a somatic differentiation, which is usually of a permanent nature and can be propagated vegetatively . With Coffea, this dimorphism is characterised by differences in growth direction of the branches. When the tip of an upright growing (orthotropic) branch, is grafted on a seedling, a normal plant is obtained, but when the growing tip of a lateral (plagiotropic) branch, is grafted in a similiar manner, an abnormal plant is produced having only lateral branches. As this phenomenon is of both theoretical and practical value a series of investigations were carried out, the preliminary results of which are presented in this paper. The nature of the buds found in the leaf axils on the main stem and lateral branches were studied and it was found that : a) on the axis beneath the cotyledons no buds were found or none were developed following cutting of the main stem below the cotyledons. b) in the axils of the cotyledons a group of dormant buds exist which can develop into orthotropic branches, when the main axis is cut below the first pair of permanent leaves. c) buds which develop into lateral (plagiotropic) branches, ordinarilly first appear in the axils of the eighth to eleventh pair of leaves. It was observed that in plants with certain genetic constitution the formation of plagiotropic branches first occurred in the 33rd pair of leaves. d) in the leaf axils on the main stem, which produce buds giving origin to a plagio" tropic branch, there also occur two or sometimes three other buds, which may develop into orthotropic branches when the main axis of the plant is eliminated. Rarely also a third type of buds occurs there which may produce flowers. e) the leaf axils of plagiotropic branches contain flower buds and buds which give origin to plagiotropic branches only and never to orthotropic branches. On coffee plants with certain genetic constitution, the flower buds do not develop but an abundant secondary branching at the time of flowering takes place. By means of several graft combinations it was possible to show that no modifications of the original growth direction of the scion branch occur. The differentation into plagiotropic branches was found to be permanent and irreversible. The same irreversible condition was observed to be true of rooted stem cuttings of plagiotropic branches. A special study was made of Coffea arabica var. erecta, a dominant mutant, which has upright growing lateral branches. Experiments revealed that even in this coffee genotype dimorphism exists, as grafts obtained from lateral branches only formed low shrubs, in spite of the fact their branches grew upright. Even with this specific genotype it was found necessary to use the tips of orthotropic branches in order to obtain normal plant development. Several hypothesis are presented which might explain this phenomenon. Attention is called to the fact that the buds which exist close together in the leaf axils of the main stem have already differentiated into either the orthotropic or plagiotropic form and that their subsequent growth will be governed by this prior differentation.