The row number of maize ear was related to climatic parameters, soil parameters and shoot growth criteria in 3 series of situations (Tables I & II). The first consisted of 14 experiments carried out at several locations between 1982 and 1988, with favourable soil structure, plant density and fertilization. The second consisted of 8 experiments where 2 typical unfavourable structures of the ploughed layer were compared to the favourable structure (O) in each location. The first typical structure (B) consisted of dm-sized compact clods separated by cm-sized voids, and the second (C) was continuously compacted. In the third series, plant density of over 30 plants.m2 was compared to the common density (between 8 and 9 plants.m2) - in experiments with favourable conditions, the row number was variable (Table IV) and significantly correlated with air temperature during a period which began around the time of the ear leaf was initiated, and ended at the initiation of the first spikelets (Fig. 2 & 3). - the row number was neither correlated with cumulated global radiation during the same period (Fig. 2), nor with criteria characterizing plant growth (Fig. 4). - a reduction in row number was observed in plots with unfavourable soil structure (Table Va). This reduction was not correlated with the reduction in plant growth (Fig. 5). Row number might, therefore, be determined by a non-trophic mechanism.