It is now well recognised that within almost any species of pasture plants there are distinct varieties or strains which differ in certain characters such as colour, growth habit, herbage yield, disease resistance, flowering time, or persistency. Plant breeders produce bred strains that are superior in some particular characters to the strains already in existence. In pasture plants most of the plant breeding will be toward increasing the yield of herbage, so that a simple and reliable method of measuring production is essential for this work.