(d) : Equisetum is a pteridophyte and in pteridophytes, the main plant body is a sporophyte which is differentiated into true root, stem and leaves. Gametophytes are small or inconspicuous and free living, mostly photosynthetic thalloid called prothallus. Riccia is a liverwort and Polytrichum is a moss. The sporophyte in mosses is more elaborate than that in liverworts. Volvox shows oogamous type of sexual reproduction,i.e., fusion between one large, non motile (static) female gamete and a smaller, motile male gamete. During unfavourable conditions, the slime mould differentiates and forms fruiting bodies bearing spores at their tips. The spores possess true walls. They are extremely resistant and survive for many years, even under adverse conditions.