If one believes in the bryophytic ancestry of land plants, the columella in the sporophyte of Anthoceros seems to be a good starting point for the origin of vasculature. It is thus expected that the frequency of apomixis increases with latitude or from warmer to colder climatic regions. Axelrod 1959 supported the polyphyletic origin of Leclercq and elaborated it by his own palaeopalynological discoveries. All embryo-like structures were found to contain 12S storage protein, whereas preculture anthers, anthers from which embryos had been removed, and regenerated shoots did not have detectable 12S storage protein. According to Goebel 1891 plants of Selaginella grown under feeble illumination tend to produce only microsporangia in their strobili.
However, there are two schools of thought about their origin. The nutrition is either autotrophic when chlorophyll is present or saprophytic when mycorrhiza is present. This type of stele is seen in Rhynia. According to majority of workers the bryophytes have been originated from Chlorophyceae which are commonly found in fresh waters and rarely in sea waters. Spores are haploid and are produced in sporangia. It divides transversely to form an outer and an inner cell Fig.
There is a great variety in the nature and organisation of the sporophytic plant body in pteridophytes. However, despite the significant role played by apogamy in fern evolution and diversification, the distribution pattern of apogamous ferns and lycophytes has received little attention. The germination and development of the gametophyte is different in homosporous and heterosporous forms. In none of the algae the egg is surrounded by any cellular jacket as it is always enclosed within a protective layer jacket layer in the case of bryophytes. The function of the suspensor is to push the developing embryo deep into the gametophytic tissue so that it can easily absorb nutrition. It has to sustain itself first and only then comes the perpetuation of the race. Moreover, and from a more general point of view, many organisms with haploid-diploid life cycles exhibit the phenomena of apospory the transition from sporophyte to gametophyte without meiosis and apogamy the transition from gametophyte to sporophyte without gamete fusion in which there is a clear uncoupling of cellular mechanisms that affect ploidy and the alternation between the sporophyte and the gametophyte Bell, 1992.
The lycopsid stock gave rise to coniferopsida. Sporophytic Generation of Pteridophytes: It is the sporophytic generation which constitutes the main plant body in pteridophytes. These plants are classifi ed, according to their sexual system, as monoicous and dioicous, with a few lesser categories recognized by bryologists. Genes triggering ectopic embryo development on vegetative sporophytic tissues are well described; however, a genetic control of embryo development from gametophytic tissues remains elusive. We propose that flo interacts in a sequential manner with other homeotic genes affecting floral organ identity. Dry fronds of many ferns make good litter for livestock.
Contrariamente, los polipodios seleccionados en este estudio aparentemente no desarrollaron anteridios y por lo tanto, no se observaron esporófitos, a excepción de P. Further, some of the fossils of early pteridophytes were quite complex and not simple strobiloid plants as Bower liked them to be. The colonization and radiation of multicellular plants on land that started over 470 Ma was one of the defining events in the history of this planet. Systematics of ferns have been specially studied by Chowdhury 1937 , Alston 1945 , Gupta and Bharadwaj 1957 , Panigrahi and Chowdhury 1961 and Abraham et al 1963 etc. An emerging, albeit surprising, consensus based on recent molecular phylogenies is that hornworts are the closest extant relatives of tracheophytes Qiu et al.
In addition, the concentrations of sucrose, glucose, and fructose were measured for each stage of ovule development, both for sexual and apomictic plants. Leaf primordia also can be excised and cultured. According to Bell 1964 these lysosomes destroy in spore the parental characters sporophytic characters in spore and gametophytic characters in egg and invest them with characters of new generation. The plant body here is a naked, branched axis with no evidence of roots. The morphogenic development of gametophyte Cheilanthes bonariensis is described from spores collected in the municipality of Tlaxco, Tlaxcala, Mexico.
After the root grows into the soil the sporeling separates itself from the gametophyte and grows independently. The dispersal units of plants are seeds but pollen is also dispersed and there are many similarities to be found between these two types of diaspores, especially in their environmental interactions. In these ferns, there is a lack of sexual reproduction and the gametophyte and sporophyte have the same chromosome number. As has been pointed out in the preceding paragraph, the female gametophyte is reduced to such an extent that it never outgrows the limits of the megaspore. The leaves and branches arose later as a modification of the axis. Subsequently the main vasculature of the stem gave out a branch which ran up to the base of the leaf only. The cortex is either parenchymatous or may have sclerenchyma also.
Anthocerotean Theory: Campbell 1895 and Smith 1938 are the chief supporters of this theory. The transfer of apomixis into sexual crops will allow the production of self-perpetuating improved hybrids, and the fixation of any desired heterozygous genotype. Sometimes there will be an outermost epispore and a middle mesospore in addition to exine and intine. It appears unlikely that there are any truly completely apomictic plants, as low rates of sexual reproduction have been found in several species that were previously thought to be entirely apomictic. The main plant body is sporophytic and forms a dominant phase in the life cycle. In the presence of kinetin, a supposedly gametophytic bud inducing substance, the secondary protonema of the moss Physcomitrium pyriforme Brid. This is a boon to a gametophyte on the terrestrial habitat and forms a good starting point for the development of embryo than an independent pro-thallus which has to meet successfully the challenges of a terrestrial environment for survival.
Among the different types of protosteles, haplostele is regarded as the most primitive and the mixed protostele as the most advanced. Further, in certain cases, competent cells may be switched either into sporophytic or gametophytic developmental pathways depending upon the nature of the stimulus. Indeed in its ideal location and to some extent in its function, through not in structure the columella of the sporophyte of Anthoceros tempts any one to consider it as a precursor of the vasculature. But there are many instances of such apogamous sporophytes having 2 x number of chromosomes. The pattern of gametangia and sporophyte development was different among the species, but the same between the sites.