To solve this problem, we need to understand the types of spores produced by plants like $Selaginella$ and $Salvinia. \newline$These plants produce two kinds of spores, which are known as:$\newline \bullet$Microspores: These are smaller spores that typically develop into male gametophytes.$\newline \bullet$Megaspores: These are larger spores that typically develop into female gametophytes.$\newline$Plants that produce two different kinds of spores are referred to as heterosporous.$\newline$Let's analyze the options:$\newline \bullet$Option 1: Homosorus - This term is not relevant to the type of spores produced.$\newline \bullet$Option 2: Heterosorus - This term is not commonly used in the context of spore production.$\newline \bullet$Option 3: Homosporous - This refers to plants that produce only one type of spore.$\newline \bullet$Option 4: Heterosporous - This correctly describes plants that produce two kinds of spores.$\newline$Therefore, the correct answer is Option 4: Heterosporous.