الفهرس 
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Abstract
Mosses play important roles in both natural and scientific systems. It is necessary therefore to name moss species that play these roles. But moss species undergo hybridization, polyploidization, and morphologically cryptic genetic differentiation which make identification of mosses a big obstacle. In addition, natural phenotypic plasticity is highly recorded in response to adaptation of mosses to heterogeneous environmental conditions. Although morphological limitations between moss species are not sharp, yet morphological species concept is still most commonly utilized. Unclear species circumscriptions and identification difficulties, based on morphological characters of taxa retarded researches in ecology, biodiversity and applied uses of mosses.
A solution for these problems may be either via determining stable morphological characters subject to a minimum of environmentally induced plasticity or via recording the range of changes in characters for species under different environmental conditions. Thus, the aim of the thesis was to record the range of morphological plasticity of four species; Bryum argenteum Hedw., Bryum subapiculatum Hampe, Funaria hygrometrica Hedw. and Philonotis hastata (Duby) Wijk & Margad., in light of different percentages of soil maximum water holding capacity and/or various nutrient concentrations in media and determining the stable characters, if found. Mosses are affected by changes in their microhabitats however, the correlation between a particular change in a wild habitat and its effect on a moss plant is quite a problem, which can be solved by the in vitro cultivation under controlled conditions.
In the present work, the first aim was to develop a successful method for cultivating mosses starting from gametophores. After several trials, axenic cultures were obtained without using chemicals in the sterilization of the gametophores but only washing by sterilized distilled water. It was a successful method, as the obtained survival percentages, ranged from (67%-100%) for B. argenteum and (33%-100%) for both B. subapiculatum and P. hastata. These percentages represent a very high success percentage in the axenic cultivation of gametophytes.
The second and main target was to record morphological changes of Bryum argenteum, B. subapiculatum and Funaria hygrometrica and Philonotis hastata in response to controlled changes of soil maximum water holding capacity and/or nutrient concentrations under in vitro cultivation. Generally, plasticity is either morphological and/or physiological but, in this work focus was on morphological plasticity only. Approximately 30 different characters of protonema and gametophores were recorded.
The variation of B. argenteum in response to soil water holding capacity was in the branching pattern, while its variation was mainly in the morphology of leaves -their shapes and structure- within gametophore and among gametophores in response to nutrient concentrations.
B. subapiculatum showed slight variation in response to changes in nutrient concentrations. It was difficult to study its response on soil due to the growth of cyanobacteria and diatoms as contaminants.
The response of F. hygrometrica to changes in soil water holding capacity seemed to be changes in stem length and some leaves characters.
P. hastata showed high morphological plasticity but no vegetative reproduction ability in the absence of nutrients, while it showed almost the reverse in their presence.
In the genomic era, another solution for the problems of moss identification was to depend on molecular information and DNA barcoding which are more accurate and largely independent of morphology. The third target was achieved via confirming the identification of species under study by molecular sequencing for nuclear (ITS) region only or with chloroplast (rbcL) region. This was done via comparing sequences of specimens under study with reference sequences of identified specimens in the database and constructing the phylogenetic trees.
The study recommended more researches in moss morphological plasticity, especially after the achieved success of the in vitro cultivation of gametophores without sterilization by chemicals. It recommended utilizing the modified technique of in vitro cultivation in studying the ability of mosses to produce antibiotics and biopharmaceutical proteins.