Ovule or Female Flower of Gnetum

 

Ovule or Female Flower of Gnetum:-

> Each ovule consists of a nucellus surrounded of three envelopes. The nucellus consists of central mass of cells. The inner envelope elongates beyond the middle envelope to form the micropylar tube or style. The nucellus contains the female gametophyte. There is no nucellar beak in the ovule of Gnetum.

Stomata, sclereids and laticiferous cells are present in the two outer envelopes.

> Madhulata (1960) observed the formation of a circular rim from the outer epidermis of the inner integument in G. gnemon. Thoday (1921), however, observed the formation of a second such rim at a higher level. The ovules in G. ula are stalked.

Morphological Nature of Three Envelopes:- Several different views have been given by many different workers regarding the morphological nature of the three envelopes surrounding the nucellus. A few of them are under mentioned:

i. According to Strasburger (1872) three envelopes of nucellus are integuments developing from the differentiation of single integument.

ii. Baccari (1877) opined that the outer envelope is a perianth while the inner two envelopes are integuments.

iii. Van Tieghem (1869) considered the two inner envelopes as the integuments while the outer envelope as an ovary or analogous to it.

iv. According to Lignier and Tison (1912), however, the outer two envelopes form a perianth while the inner envelope is equivalent to an angiospermic ovary. Vasil (1959) also supported the view of Lignier and Tison (1912) in case of Gnetum ula.