Thalamus is the direct prolongation of the pedicel and is also called torus or receptacle. It may be elongated and conical or like an inverted cone with a spongy flat top as in lotus.
It may be slightly convex as in brinjal or as in Artabotrys, Michelia, etc. and cup-shaped as in epigynous flowers.
In most of the flowers, thalamus has three internodes which are condensed. When it is elongated, the first internodes (between calyx and corolla) are called anthophore, the second internodes (between corolla and androecium) are called androphore or gynandrophore and the third internodes (between androecium and gynoecium) is known as gynophore.
Gynophore is seen in the flower of Capparis sepiaria. Androphore or gynandrophore is found in Passiflora suberose (F’ig.11.1.31). Sometimes the thalamus projects into the ovary and the carpels remain attached to it which a separated at maturity. This type thalamus is called carpophores, e.g… Foeniculum.
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The floral leaves are inserted on the thalamus. If it is inserted successively such as calyx, corolla, androecium and gynoecium and it is terminated by the gynoecium the flower is termed as hypogynous, i.e, ovary is superior.
It is very common and found in Magnolia, mustard brinjal, etc. In case of cup-shaped concave thalamus, the gynoecium is placed at the centre of the cup. It is, called perigynous and here ovary is half superior and half inferior.
The other three whorls are inserted on the rim of the flat or the concave thalamus, e.g., peas, strawberry, rose, etc. In the third type of insertion of the floral whorls on the thalamus, it is found that the cup shaped thalamus may fuse with the wall of the ovary giving it the lowest position.
The other floral whorls remain above the ovary and in this case, the ovary is said to be inferior. This condition of insertion of floral whorls, in relation to the thalamus is called epigynous, e.g., sunflower, guava and the unisexual pistil late or female flowers of Cucurbita, etc.