SUMMARYGrass, after (a) mincing, (b) chopping (to 1–3 cm), and (c) neither treatment, was ensiled at 30° in the laboratory. The growth of Gram‐negative organisms and of each of the main groups of lactic acid bacteria was fastest in the minced material and slowest in the untreated. Mincing had the special effect of permitting the multiplication of lactic acid bacteria when other silage organisms were losing viability. The pH value decreased much more rapidly and to lower levels in minced silage than it did in silage of untreated grass. Variations in response to the treatments were associated with differences in the bacterial populations on the fresh grass and with properties of the grass. Silage made in larger quantities in concrete silos from untreated or lacerated grass of high sugar content had a bacterial population dominated by lactobacilli and was of low pH irrespective of the treatment applied. Silage made at 30° in the laboratory from the same herbage showed that the effects of laceration were considerable and similar to those of mi