This article deals with the influence of the lateral boundaries on the Rayleigh-Benard problem. The natural convections in the containers with the geometry of seetoriai cylinder are analysed by the linear stability theory. The critical Rayleigh numbers are determined for the onset of natural convection of fluid in the cylindrical containers heated from below and cooled from above. The preferred convection modes at Rayleigh number just above the critical points and the influence of the lateral walls in them are dealt with.