Q.15. Describe the microsporoplyll of Cycas. (2009)
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Q. Describe the structure of Cycas Microsporophyll. (2010)
Ans. Microsporophyll or male cone of Cycas: -
The male cones of Cycas usually occurs singly in the centre of crown. It is woody, wedge shaped blunt long. The male cone of Cycas is among the largest reproductive structure in the Gymnosperms. Each male cone consist of an axis on which the sporophylls are arranged spirally. These sporophyll is known as Microsporophylls or stamens. Each microsporophyll is a flattened structure narrow below and explanded above into the expanded sterile disc the apophysis. The upper portion of the microsporophyll is smooth and sterile on the lower adaxial side microsporangia (pollen sac) are borne is soral groups of three to six known as microsori. They dehisce by a slit which extends radially from centre of a sorus. The number of microsporangia or pollen sacs on the single microsporophyll is variable. The microsporangium is a blobular or ovate body with several layered wall. It contains, numerous microspores or pollen grains.
Development of microsporangium and microspores: -
The development of microsporangium is eusporangiate type. The microsporangium develops from a single hypodermal cell of microsporophyll.
The initial cell divide periclinally into an outer sterile or primary wall cell and inner primary sporogenous cell or archesporium. The primary wall cell divides by repeated periclinal and anticlinal divisions. A sporangium wall several cells in thickness is developed which is covered over by epidermis. The epidermis later becomes thickened and two rows of elongated cells mark the line of dehiscence. The primary sporogenous cell also divide repeatedly and form a large mass of sporogenous cells or spore mother cell. From the periphery of the sporogenous tissue and tapetum is differentiated. As the development proceeds the sporagenous cell round off and becomes isolated as spore mother cells. The spore mother cells begin to float in a nutritive medium formed by the disorganisation of the tapetum. The spore mother cells divides by a reduction division (Meiosis) and followed by a simple division so as to form four microspores or pollen grains. Thus the microspores get developed which are haploid and since regarded as the first cell of the male gametophyte.
Q. 16. Describe with the help of diagram the megasporophyll of Cycas. (2005)
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Q. Describe the external structure of megasporophyll of cycas. (2013)
Ans. Megasporophyll or Female Cone of Cycas: -
The genus cycas is peculiar in its ovulate strobilus in that, it is not a true compact cone strobilus but simply a rosette of megasporophylls arising spirally in acropetal succession and loosely arranged on the stem in a rosette the ordinary crown of foliage leaves around the stem tip. The apical meristem remains uneffected and continue to grow so as form future, leaves and sporophylls. Megasporophylls replace scale leaves and are morphologically equivalent to them. The megasporophylls of Cycas are large and show that they are leafy in nature. Each megasporophyll is brownish pelmate structure bearing few ovules on the stalk.
Megasporophyll has more or less distinct part :
(i) A proximal short or long stalk like axis.
(ii) A middle portion bearing two rows of opposite and alternately arranged ovules.
(iii) A distal more or less expanded, dorsiventrally, flattened sterile portion of varying shapes. In most cases megasporophylls are covered with yellow or brown hairs.
There occurs a great variation with regard to the size and shape of the megasporophylls in different species of Cycas. The megasporophylls of C. revoluta are prinnate whereas those of C. circinalis, C. rumphii and C. beddomei are obovate or laciniate structures.
In C. pectinata and C. siamensis they are orbicular or rhomboidal structures. They usually measure 15-25 cms. in length. In the upper part of the stalk are present 1-6 pairs of ovules, laterally. This number is variable in different species.
Q.17. Describe the economic importance of cycas. (2012, 13)
Ans. Economic importance of cycas: -
(1) Stem of C.circinalis produce gums; a kind of sago is obtained from truck; juice of leaves is helpful for vomiting and flatulence; seed and bark ground to a paste and mixed with coconut oil, serves as poultice for swelling and sores.
(2) Cycas evoluta is said to be a tonic and expectorant : roots have strachy material; seed meal is washed, cooked and eaten.
(3) Stem of cycas rumphii yield sago.
(4) Cycas pectinata yield edible fruits, so cycas is of economic importance.