 The ascus is a tube-shaped vessel, a "meiosporangium", which contains the sexual spores produced by meiosis and which are called "ascospores".Apart from a few exceptions, such as "Candida albicans", most ascomycetes are haploid, i.e., they contain one set of chromosomes per nucleus.During sexual reproduction there is a diploid phase, which commonly is very short, and meiosis restores the haploid state.