The essential study in this paper is the examination of seasonal and yearly changes in the growth rate of pastures and pasture species in different districts, on different soils, and over a number of 'years. It is impossible to deal with all aspects of the subject adequately in the time available, and I have therefore not considered in detail how or why these growth rate changes occur, -but have confined: discussion to an analysis of the differences in pasture growth rate that exist in varioiib parts of New Zealand. Again, because the measurement trials of the",Department of Agriculture' have so far been restricted td the Iiat and easily rolling country, comparisons are available only between better-than-average pastures under better-than-average management in the more productive districts of New Zealand. With the possible exception of some of the trials in Canterbury, all the pastures concerned are or could have been made dominantly ryegrass and white clover.