In this essay we will discuss about:- 1. Roots of Glossopteris 2. Leaves of Glossopteris 3. Fructification.
Essay # 1. Roots of Glossopteris:
The detached roots of Glossopteris plant are called Vertebraria (Fig. 1.9B). The roots are flattened and grooved with wedge-like sectors that radiate from the centre of the axis.
The wedges are made up of secondary xylem which covers the central polyarch protoxylem. The pycnoxylic secondary xylem strands alternate with protoxylem strands (Fig. 1.9C). In young stage, the cavities that formed between the radiating arms suggest that the plant grew in semiaquatic environment.
Essay # 2. Leaves of Glossopteris:
Glossopteris (Fig. 1.9D) leaves are simple, entire and sessile (rarely petiolate, e.g., G. petiolata). Leaves show a great variation in size and shape (linear lanceolate to spathulate ovate). They have a strong midrib from which numerous longitudinally running veins pass out to form a reticulate pattern or remain free.
Leaf anatomy shows a typical dorsiventral and hypostomatic nature with irregularly dispersed haplocheilic, sunken stomata. Some species show a- hypodermal layer. Mesophyll is differentiated into palisade and spongy parenchyma. Some scale leaves (rounded or lanceolate) are found to be associated with Glossopteris leaves.
Some other less common leaf genera namely, Gangamopteris, Palaeovittaria, Rubidgea, Euryphyllum, Rhabdotaenia are also included under Glossopteridaceae family due to their identical form, venation pattern and cuticular structure.
Gangamopteris (Lower Permian) leaf is identical to Glossopteris except the absence of well.-defined midrib (Fig. 1.9E). Rhabdotaenia is distinguished from other leaf genera due to the presence of non-anastomosing lateral veins.
Essay # 3. Fructification of Glossopteris:
Male Fructifications of Glossopteris:
Eretmonia (Fig. 1,9F) pollen organ consists of a fertile petiolate lamina of triangular to rhomboidal in outline. Two branches bearing whorls of microsporangia are borne on upper part of the lamina. After dehiscence, the sporangia look purse-shaped due to the longitudinal rupture.
The most common pollen organ, Glossotheca, is basically similar to Eretmonia, except it has 2-3 sporangia-bearing pedicels. Each pedical bifurcates into two daughter branches containing clusters of elongate sporangia at their tips.
Kendostrobus is another pollen organ associated with Glossopteris leaf. It is a long, stalked, cylindrical structure having a central axis with spirally arranged naked exannulate sporangia in groups.
The isolated sporangia of Glossopteris are known as Arberiella, Lithangium and Polytheca. Pollen grains are bisaccate, striated in Arberiella, monolete in Lithangium and trilete in Polytheca.
Female Fructification of Glossopteris:
The dorsiventral structure bearing seeds of Glossopteridales are variously termed as capitulum, megasporophyll, cupule, fertiliger or cladode.
Scutum (Fig. 1.9G) has been described by Mrs. Plumsted (1952). This lanceolate to ovate fructification is attached by a pedicel to the lower portion of Glossopteris leaf midrib. It has two bilaterally concave symmetrical valves. A wing-like expansion is present along the line where the two valves join. Small sac-like structures are present in the concavity of both the halves.
The fructification as described by Plumsted is to be bisexual where the lower sacs represent seeds and the upper ones pollen sacs bearing monolete, non-winged pollen. But according to many authors, the Scutum is a female fructification where one half of the unit represents a receptacle that contains a large number of ovules on elevated projection.
The other half represents a fertile scale that protects the ovules at early age and detaches later to expose micropyle for receiving pollen grains during pollination. Some other authors argued that the ovules of Scutum were borne on a single fleshy structure and the appearance of two parted structures is due to the splitting of rock through the middle of the ovule-bearing organ.
Ovulate structure of Denkania indica (Fig. 1.9H) was reported from Raniganj stage (Permian) of India. In this organ, six long pedicellate seed-bearing cupules are attached to the adaxial surface of the midrib of Glossopteris leaf. Apparently, one seed is produced per cupule comprising of two appressed scale-like valves.
Lidgettonia is another compound ovulate structure consisting of a spathulate leaf with two rows of disc like capitula attached abaxially on the petiole.
Ottokaria is an ovulate fructification attached to Gangamopteris leaf by a slender stalk. It consists of a flattened capitulum with a marginal frill bearing a large number of ovules on the under surface.
Some other ovulate structures of glossopterids like Dictyopteridium, Partha, Rigbya, Plumsteadia, Senotheca, Rusangea, etc., have been described by various authors.