**Ploidy of Endosperm in Pteridophytes**

In pteridophytes, the endosperm is triploid (3n). The endosperm is a nutritive tissue that is formed within the embryo sac (female gametophyte) after double fertilization.

**Formation of Endosperm:**
1. Double Fertilization: In pteridophytes, double fertilization occurs where two sperm cells are involved. One sperm fertilizes the egg cell to form the zygote, which develops into the embryo. The other sperm fuses with the two polar nuclei present in the central cell of the female gametophyte, leading to the formation of the endosperm.

**Ploidy of the Endosperm:**
1. Two Haploid Nuclei: The fusion of the sperm with the two haploid polar nuclei results in the formation of a primary endosperm nucleus.
2. Triploid Nucleus: The primary endosperm nucleus undergoes several rounds of mitosis without cytokinesis, resulting in the formation of a multinucleate cell called the endosperm. The endosperm nucleus becomes triploid (3n) as it contains three sets of chromosomes from the union of the haploid sperm and two haploid polar nuclei.

**Function of Endosperm:**
1. Nutrient Storage: The endosperm serves as a storage tissue, providing nourishment to the developing embryo. It stores nutrients such as starch, proteins, oils, and minerals, which are essential for the growth and development of the embryo.
2. Nutrient Transfer: As the embryo develops, it utilizes the stored nutrients from the endosperm for its growth. The endosperm transfers these nutrients to the developing embryo through the vascular tissues.

**Significance of Triploid Endosperm:**
1. Genetic Balance: The triploid nature of the endosperm helps in maintaining genetic balance in the plant. It ensures that the embryo develops properly by providing a sufficient supply of nutrients.
2. Increased Nutrient Storage: The triploid endosperm allows for increased storage capacity, enabling the plant to accumulate a higher amount of nutrients for the developing embryo.
3. Enhanced Seed Viability: The presence of a well-developed endosperm contributes to the viability and germination of the seed, as it provides the necessary nutrients for the growing embryo until it can establish its own photosynthetic capabilities.

Overall, the triploid endosperm in pteridophytes plays a crucial role in supporting the growth and development of the embryo by providing a nutrient-rich environment.

Endosperm is not present in pteridophytes. They are seedless plants, no endosperm is formed.