Q.12. Describe alternation of generation in Pinus.
Ans. Alternation of Generation in Pinus: -
The adult plant is pinus represents the sporophytic phase of life cycle. The sporophytic plant body of pinus reproduces sexually by means of spores and after passing through gametophytic phase of life cycle again produces sporophytic plant. Thus by the following account we will see that pinus plant shows a distinct alternation of generation. In the life cycle the sporophyte phase is of long duration and is represented by the huge pine tree which bears the staminate and ovulate cones. The staminate cone produces pollen grains in pollen sacs on the microsporophyll. The female cone produces megaspores one in each ovule borne on the upper surface of the ovuliferous scale. Since meiotic divisions occur at the time of the differentiation of the pollen grains and megaspores, the latter structures represents the first cells of the second generation the gametophytes. Both the gemetophytes in Pinus are further reduced and are parasitic upon the sporophyte. They are retained within the respective spores. The vegetative or sterile phase of the male-gametophyte is represented by the prothallus cells. The female gametophyte, consists of an extensive tissue forming the female prothallus but its chief function is to provide nutrition to the embryo. It obtains the, food for this purpose from the sporophyte plant. It is enable to carry on independent assimilation.
The most remarkable feature is that it is retained within the sporophyte tissue the nucleus and not discharged. The microgametophyte is carried by the wind to a position in the vicinity of the ovule from where, it is shifted on to the apex of the nucleus. It then puts out a pollen tube which carries the male gametes on to the archegonia developed at the micropylar end of the female prothallus. The male gametes unite with the egg in the archegonium to effect fertilization. The fertilized egg is diploid structure. It is the first cell of the future sporophyte. It develops into the embryo which is the new sporophyte.
Q.13. Differntiate between the seeds of Cycas and Pinus. (2006)
Ans. Differences between Seeds of Cycas and Pinus
Q.14. Describe the economic importance of Pinus.
Ans. Economic Importance of Pinus: -
Pinus is chiefly valued for the wood which is used for building materials, furniture, poles, match boxes, and other articles. Besides the above uses the wood is also used as a fuel as it can be easily ignited due to the presence of resin. Female cones after they have released the seeds are collected by the hill people and used as fuel during winter. Although several species of Pinus yield wood but the wood of P. excelsa (kali) and P.longifolia(chir) are more important for timber.
The plants yield large amounts of resin from their old stems which are used in resin and turpentine industry. Resin and turpentine are obtained after the distillation of the wood and are used for paints, varnishes and medicines.
The seeds of P. gerardiana are edible and are sold in the market under the name chilgoza. The seeds of P.roxburghii are also edible.
Many species of Pinus are important as cheap sources of cellulose which is used for various industrial purposes. Pine forests usually surround the sanatoria and make the surrounding atmosphere attractive and healthy for the patients of tuberculosis.
Among the Indian species P. gerardiana provide edible seeds, P.roxburghii and P.wallichiana are important sources of timber and P. insularis and P. roxburghii yiled resin and turpentine. A majority of species are planted for their beautiful appearances.
Q.15. Differentiate between wood of Cycas and Pinus Wood. (2011)
Ans. Differences between wood of Cycas and Pinus
Q.16. Give an account of morphology and geographical distribution of Ephedra.
Ans. Systematic position: -
Division - Gymnospermae
Class - Gnetopsida
Order - Gnetales
Family - Ephedraceae
Genus - Ephedra
Distribution: -
It has nearly 42 species widely distributed in eastern and western hemisphere. The plant occurs in central and Western Asia, New Mexico, Arizona and America.
In India, it is common in sub-alpine Himalayas, alpine region of Western Tibet, Sindh - Punjab, U.P. and Rajasthan. Plants grow between altitude of 2000 - 5000 metres.
Ephedra : (A) Plant showing shrubby habit, (B) A portion of plant enlarged
Following six species are commonly found in India:
1. E. foliata: - It is common in Punjab, Rajasthan and Sindh.
2. E. geradiana: - It is common in Himalayas spreading from Kashmir to Sikkim.
3. E. intermedia: - It is common in Punjab, Himanchal Pradesh and Kashmir.
4. E. saxatilis: - It is found in Sikkim.
5. E. nebtodensis: - It is found in Kashmir.
6. E. regiliana: - It is common in NEFA areas (Ladakh and Lahul).
External Morphology: -
The sporophytic plant body is well branched xerophytic shrub with jointed stem, stem is climbing in E. Holiata. Stem is hollow and photosynthetic. Riszome may be present in E. trifurca. Foliage leaves are absent. Three or four scale leaves are present at each node in some species arranged in opposite and decussate manner. The scale leaves are united at base forming sheath. Each scale leaf has a mid-rib stomata are rarely present in it. Root are tap roots.
Internal. Morphology: -
Stem - In transverse section the outer surface of the stem shows ridges and furrows. Epidermis is thick-walled. It is covered by a thick layer of cuticle. At places it is punctured by haplocheilic stomata, each of which is sunken in a circular pit in the furrow between the ridges. Hypodermis is represented by a group of very thick walled cells (fibrous cells) lying under each ridge. The cortex is differentiated into an outer palisade layer and an inner spongy tissue. The cells of both palisade and spongy tissue possess chloroplasts and are provided with intercellular spaces.
The innermost layer of the cortex represents will defined endodermis. It surrounds the endarch siphonostelic vascular cylinder. Pericycle is not well demarcated. Vascular bundles are collateral. The cambium occurs in between the xylem and the phloem.
Pith is usually parenchymatous. At or near the nodes pith is composed of strongly lignified cells which form a peridermal diaphragm.
Secondary Growth - It takes place by persistent cambium. The wood formed is not thick.
The wood consists of tracheids and vessels showing single row of bordered pits radially and Bars of Sanio, both on radial and tangential walls. Vessels originate independently. Vessels are large in size and abudant in spring wood than in autumn wood. Annual rings are frequent. Medullary rays are uniseriate in young stages but become multiseriate in older stems.
The cork cambium or phellogen develops deep into the cortex. It produces cork- the periderm on outer side.