Let X be a smooth projective variety over the complex numbers. Recall that a Cohen-Macaulay curve is a one-dimensional closed subscheme without embedded or isolated points (fat components are allowed). >I want to show that if you fix a curve class β in H<sub>2</sub>(X), then there is a bounded interval which contains the genus of every CM curve whose homology class is β. > >Do you know of a reference for this result? Motivation: I am trying to prove a certain class of sheaves forms a bounded family (namely, the collection of sheaves underlying <a href="http://arxiv.org/abs/0707.2348">stable pairs</a>). The above result will allow me to reduce to the case where the support is a fixed CM curve, and from there, I know how to finish the proof. I am aware that Le Potier (who built the moduli space of stable pairs, among others things, in "System Coherents et Structures de Niveau" --- pardon my lack of accents) has proven a much stronger result. However, for my purposes, it would be very helpful to have a proof (hopefully much less technically demanding than Le Potier's) that is no more general than what I need. EDIT: in hindsight, and in light of the negative answer below, I realize that Le Potier does not claim to prove quite what I claimed he claimed.