2018 Solved Old Paper (BOT-202) New

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Male Fructifications of Glossop­teris:-
> 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.
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Pentoxylales:-
Characters of Pentoxylales:-
1. Extinct Mesozoic plants found in Jurassic period.
2. Although the exact habit of these plants is not clearly established, these were probably shrubs or very small trees.
3. Long and short shoots were present on these plants.
4. Short shoots had spirally arranged leaves and terminally located reproductive organs.
5. Leaves were thick, simple, lanceolate, and had diploxylic leaf trace.
6. Stomata were formerly thought to be syndetocheilic, but now they are considered to be haplocheilic.
7. Leaves possessed open venation.
8. Stems were polystelic. Basinger et al. (1974) opined that “it may be more appropriate to call each stele as vascular segment or sympodium”.
9. Wood of Pentoxylon was pycnoxylic and resembled Araucaria.
10. Ovules were sessile.
11. Female reproductive organs were like stalked mulberry, consisting of about 20 sessile seeds attached to central receptacle and surrounded by stony layer and then fleshy outer layer of integument uniting them.
12. Male reproductive organs or microsporophyll’s form whorl of branched micro-sporangiophores.
13. The micro-sporangiophores were fused basally into a disc-like structure.
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Embryo Sac of Gnetum:-
> Lotsy described the embryo sac of G. gnemon as showing an interesting deviation from those in other species of Gnetum. 
> Instead of containing only free nuclei at the fertilization stage, the embryo sac of G. gnemon was described as containing a compact antipodal tissue, sharply distinct from the micropylar chamber with its free nuclei. 
> As a consequence, the embryo sac of G. gnemon has been used ever since as illustrating a female gametophyte intermediate in structure between the tissue-filled sacs of Ephedra and Tumboa on the one hand, and the sacs of other species of Gnetum, which contain only free nuclei. 
> Later the same investigator in reporting parthenogenesis in G. ula described the embryo sac of that species as being of the G. gnemon type.
> At an early stage of the embryo sac, eight nuclei are observed grouped near the center, the sac being invested by the loose tissue of the nucellus. 
> At a somewhat later stage the nucellar cells at the chalazal end of the sac are strikingly differentiated, becoming more and more compactly arranged, gradually obliterating the intercellular spaces, and taking on the appearance of glandular cells.
> As vacuolation proceeds in the sac and the free nuclei become parietally placed, this "pavement tissue" becomes more compact and extends deeper into the chalaza.
> Still later it spreads laterally below, until it becomes fan-shaped in section, but it is always very distinct in contour and sharply marked off from the surrounding nucellar tissue. 
> At the fertilization stage the sac contains only free nuclei, which become somewhat grouped at the antipodal end, but there is no walled tissue. 
> Spreading below the sac, however, the mass of nucellar pavement tissue shows a definite contour, which might be merged in imagination with that of the sac and thus mistaken for a compact tissue within the antipodal end of the sac. 
> It will be noted that after the fertilization stage is reached (fig. g) the pavement tissue begins to lose its glandular character; and later it is destroyed entirely by the growing endosperm.
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Male strobilus:- 
> In Gnetum, the male cones are compact and slender axis-like structures, which are up to 6 cm in length. Each cone is generally a penicle that is either solitary and axillary or fascicled at the apex. The axis of the strobilus bears opposite and connate bracts. Bracts are arranged one above the other to form collars or cupules. There are 6-25 cupules are present, each cupule, staminate flowers are arranged in several definite rings, usually 3 to 6 in number.
> Each mature microsporophyll consists of a stalk bearing two unilocular microsporangia (anthers). The stalk is invested at the base by a perianth.
> In Gnetum ula, 2-4 anthers are there which are formed from microsporangial initial cells. It divides periclinally and anticlinally to form a primary cell wall, tapetal cell, and sporogenous cells. Sporogenous cells later differentiate into spore mother cells. Microspore mother cell forms microspores (pollen grains) through meiosis.
> The wingless pollen grains are liberated by the longitudinal dehiscence of the anthers.
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Stem Genus Pentoxylon Sahnii:-
> Pentoxylon sahnii and Nipanioxylon guptai are the stem genera of “Pentoxyleae”. The stems of Pentoxylon sahnii attained a diameter from 3mm to 2 cm. The stem has always been reported in association with the leaves called Nipaniophyllum.
> Presence of five steles in a cross- section of the stem has been the main reason for giving the name Pentoxylon to the genus. Many short lateral shoots or dwarf shoots were also present on the stem.
> Five steles occupied greater part of the stem in a cross-section. Each stele had its own cambium. The cambium was uniformly active in the young stems, but at maturity more secondary tissue developed towards the centre, and thus the secondary wood appeared eccentric.
> Primary phloem and primary xylem were present towards outer and inner sides of the cambium, respectively. Six steles have also been observed by Sahni (1948), although rarely. According to Vishnu-Mittre (1953) the number of steles varied along the length of the stem.
> There were present five much smaller bundles just alternating with the main bundles of the stem i.e. five steles. Each such bundle had a large amount of secondary wood. These were probably the leaf trace bundles.
> Medullary rays of the main steles were uniseriate, and they lacked ray tracheids, wood parenchyma and resin canals. The secondary wood resembled greatly with that of Araucaria. Uniseriate or bi-seriate bordered pits were present on the radial wall of tracheids.
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Affinities of Bennettitales:-
Resemblances of Bennettitales with Ferns:-
• Bennettitalean plants had multicellular ramenta on their entire body, a characteristic also seen in
ferns.
• Some other features suggesting the filicean affinity of Bennettitales include the presence of:
(i) Direct leaf traces,
(ii) Scalariform tracheids, and
(iii) Large pith.
Resemblances of Bennettitales and Cycads:-
• Bennettitales resemble cycads in the:
(i) structure of their fronds,
(ii) presence of short stems covered with an armour of persistent leaf bases,
(iii) presence of barrel-shaped trunk,
(iv) presence of very thick cortex, relatively thin wood and large pith in the stem,
(v) manoxylic wood,
(vi) monocolpate pollen grains,
(vii) orthotropous ovules, and
(viii) dicotyledonous embryo.
Resemblances between Bennettitales with Pteridospermales:-
• Characters common in both Bennettitales and Pteridospermales include:
(i) Presence of ramenta] hairs,
(ii) Syndetocheilic stomata,
(iii) Direct leaf traces,
(iv) Similar anatomical details,
(v) Leafy microsporophyll’s, and
(vi) Presence of cupule.
• The so-called bisporangiate ‘flower’ of Bennettitales could be compared with the bisporangiate fronds of Ptendospermales. 
• Scientists are of the opinion that there exist two lines of evolution from Pteridospermales. Of these, one line gave rise to Bennettitales possessing both uni- and bisporangiate forms, and the other gave rise to mono-sporangiate forms of cycads.
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a. Male Strobilus and Male Flower:-
- A male or microsporangiate strobilus or male cone is a compound structure bearing a quadrangular cone axis. It contains several bracts or cone scales arranged in opposite decussate manner. In the axil of each subtending bract is present a male flower.
- Two lateral bracts and a perianth are also present in each male flower. The perianth is formed from two bract-like anterior-posteriorly placed structures.
- Inner to the perianth is present a whorl of six micro-sporangiophores which remain fused at the base to form a cup-like structure. A sterile ovule with a single integument is present in the centre of each male flower.
- At the top of each micro-sporangiophore is present a synangium. Each synangium is formed by the fusion of three microsporangia. Each microsporangium contains many pollen grains which are shed through a vertical slit. Pollination is effected either by wind or by insects.
b. Female Strobilus and Female Flower:-
- The female strobilus, also called ovulate or megasporangiate strobilus or ovuliferous cone is also a compound structure like male cone. The axis of the female strobilus bears many broad decussate bracts or cone scales, in the axil of each of which is present a female flower.
- Inside the subtending bract of each female flower are present two small lateral bracts, two envelopes and a single nucellus. Out of the two envelopes the inner one functions as a true integument, and prolongs in the form of a long tubular micropyle.
- The outer envelope develops from two posterior-anterior primordia which fuse with each other in the early stages of the development. Some prefer to call this fusion product as perianth The perianth expands into a broad wing-like structure in the mature seed.
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Ovule of Taxus:-
- The ovule is somewhat rounded or oval in shape and orthotropous. A single thick integument is present. Integument is free from the nucellus right up to its base forming a long micropyle. The integument is differentiated into outer fleshy, middle stony and inner fleshy layers. Two vascular strands enter the integument from the base of the ovule and reach up to its top.
- A ring-like outgrowth develops from the base of the integument. It surrounds the entire ovule. It is called ‘aril’ or ‘cupule’ . Aril is green and saucer-shaped when young but at maturity it is red and cup-shaped.
- The aril also receives two vascular bundles but they are very minute and rudimentary. Pollen chamber and nucellar beak are absent in Taxus. The apex of the female gametophyte changes into a flask-shaped structure called tent-pole. The tent-pole disappears in the later stages.
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Glossopteris:- 
> Fossils of the gymnosperm Glossopteris (dark green) found in all of the southern continents . 
> Glossopteris (Ancient Greek: glossa, meaning "tongue", because the leaves were tongue-shaped). 
> The name glossopteris is first used by Brongniart.
Species:-
i. G.angustifolia 
ii. G. brasiliensis 
iii. G. browniana 
iv. G. communis 
v. G. indica 
vi. G. occidentalis 
Distribution:-
> Gondwana land was greatest ice age. 
> This condition extended from upper carboniferous to lower permian period.
> Gondwana land flora is also called glossopteris flora. 
> Gondwanaland system are of 3 types.     
a. Lower gondwana system 
b. Middle gondwana  system 
c. Upper gondwana system 
a. Lower gondwana system:- It was the luxuriant growth period of gymnosperm. It include several several speciesof Gangamopteris, Glossopteris  with Vertebraria and Gondwanadium 
b. Middle gondwana  system:- Glossopteris genera, glossopteris with vertebraria, gamopteris are included in this system.
c. Upper gondwana system:- Glossopteris genera glossopteris with vertebraria are seen in this system.
- Leaves - tongue like with reticulate venation.
- Has a central mid rib, lateral veins are arise from the mid rib and these extended to the margin. 
- Dorsiventral. 
- Seeds are borne on the sides of variably branched or fused structures.
- Microsporangia are borne on the tip of filaments ,containing large no. of pollen. 
- Seeds and pollen bearing organs were partially fused to leaves or positioned in the axils of leaves. 
- Seed bearing structures are remain within the megasporophyll. 
- It is not clear that glossopteris is monoecious or dioecious. 
- They had unusual roots called vertebraria. 
Ans.
Male gametophyte:-
> Microspore (pollen grain) is the first cell of the male gametophyte. The outer exine is thick-walled and the inner intine is thin-walled.
> In Gnetum, a microspore consists of a prothallial cell, a generative cell, and a tube nucleus. The generative cell divides within the pollen tube into two non-motile naked male gametes.
Female gametophyte:- 
> The functional megaspore is the first cell of the female gametophyte.
> In Gnetum, the megaspore mother cell takes part in the development of the gametophyte. It’s containing four megaspore nuclei and forms a female gametophyte (embryo sac). The four megaspores divide continuously and form thousands of female nuclei. The embryo sac is tetrasporic, in which 256-1500 nuclei are found.
> At this time cell wall is formed from the chalazal end. A few free nuclei in this part become larger and differentiate as eggs. Archegonia are not formed in Gnetum female gametophyte.
Fertilization:- In Gnetum, the pollen tube comes in contact with the female gametophyte and the male gamete enters the embryo sac. One gamete attaches to the female nucleus and forms a zygote. While the second gamete attaches to the other nucleus and as a result double fertilization occurs. At this time, the endosperm is formed due to wall formation at the micropylar end.
Embryo development:- In Gnetum, the zygote divides and forms two cells. Both the cells enlarge and form tubes. Each tube divides and forms suspensor and embryonal cells.
Seed germination:- Seeds are endospermic. Process of germination of the seed is hypogeal in Gnetum.