The compositions of the component parts (upper leaf, lower leaf, upper stem, and lower stem) and of the whole plant of unthinned, 6 in. thinned, and 12 in. thinned chou moellier (Brassica oleracea L.) were compared over a two-month period in autumn. Thinning decreased the dry matter contents of the whole plant and all the component parts except upper leaf but increased the crude protein contents of the whole plant and all the component parts except upper and lower leaf. The crude fibre, ether extract, mineral matter, nitrogen-free extract, and carotene contents of the component parts and of the whole plant were not affected by thinning. It was concluded that, under the conditions of this trial, thinning was not justified. In general, advancing season had little appreciable effect on the percentage composition except in the case of dry matter, which increased, and crude protein, which decreased. For the various constituents, the component parts were usually in order from highest to lowest as follows:— Dry matter: Upper leaf, lower stem, lower leaf, upper stem. Crude protein: upper leaf, upper stem, lower leaf, lower stem. Crude fibre: lower stem, upper stem, lower leaf, upper leaf. Ether extract: lower leaf, upper leaf, upper stem, lower stem. Mineral matter: lower leaf, upper leaf, upper stem, lower stem. Nitrogen-free extract: upper stem, lower leaf, upper leaf, lower stem. Carotene: upper leaf, lower leaf, upper stem, lower stem. The results obtained were comparable to data previously published elsewhere. The differences which did occur could probably be attributed to the effect of crop variety and its associated leaf to stem ratio, the age of the crop at sampling, the length of the sampling period, and perhaps other factors, such as soil fertility and climatic conditions.