A fern prothallus is bisexual. If fertilisation takes place between their gametes than it is known as

Self-fertilisation is the union of male and female gametes produced by the same individual, ie, from a bisexual individual. Cross-fertilisation is the fertilisation of male and female gametes produced by different individuals. Isogamous means fusion of isogametes (ie, of same morphology and physiology). Viviparous means giving birth to young ones.