The composition and ultrastructure of the nucellus in cotton

The nucellus of cotton was examined with the techniques of electron microscopy. Three cell types could be distinguished: (a) the micropylar cells, (b) the collar cells, and (c) the vacuolate cells. All the various types should have common features as well as distinguishing characteristics. The micropylar cells were particularly rich in multivesicular bodies which appeared to be forming from ends of the endoplasmic reticulum (ER). The plastids in these cells were highly organized and rich in a tubular component. The collar cells were distinguished by massive protein deposits within spherical swellings of the ER. The vacuolate cells had large, central vacuoles. The cytoplasm was rich in spherosomes. Unusual wall thickenings were also found in these cells. The relation of these ultrastructural features to the possible function of the cells was discussed.