In this paper we study linear relations among theta series of genera of positive definite n-ary quadratic forms with given level D, 2D, 4D and 8D for square free D. We obtain a basis for the space generated by genus theta series. This forms a basis of Eisenstein space. (c) 2006 Elsevier Inc. All rights reserved.In this paper we study linear relations among theta series of genera of positive definite n-ary quadratic forms with given level D, 2D, 4D and 8D for square free D. We obtain a basis for the space generated by genus theta series. This forms a basis of Eisenstein space. (c) 2006 Elsevier Inc. All rights reserved.