This symptom is found in plants of Pteridophyta group. In most pteridophytes, the plants where the spores are of the same type are called homosporous. But in pteridophyte plants like Selaginella and Salvinia, two types of large and small spores are formed, which are called heterospores. From large macro spores (female) and small micro spores (male), female and male gametophytes are formed respectively. In such plants, the female gametophyte remains attached to the parental sporophyte to fulfill its needs. The zygote develops in the female gametophyte, from which a new infant embryo develops. This incident is considered very important which leads to seed nature. Example Selaginella, Salvinia.