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Fruit Polymorphyism With Reference To Its Ecological Adaptive Mechanisms On 2 Species Of Ephemeral Plants

Posted on:2005-11-05Degree:MasterType:Thesis
Country:ChinaCandidate:R M QuFull Text:PDF
GTID:2120360125459294Subject:Botany
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With the aid of field observation, paraffim section techniques, scanning electron microscope (SEM) and biostatistics methods, the eco-biological characters, breeding system, megasporogenesis, microsporogenesis and the development of gametophytes, pollination biology, character of fruit-set and ecological adaptive strategies of fruit polymorphism in Heteracia szovitsii Fisch. et Mey. and Garhadiolus papposus Boiss. et Buhse., 2 species of ephemeral plant with polymorphic achenes, have been studied in this paper. The main results are as follows:1. Plants of 2 spieces are not too high with short root-system. They can germinate and grow rapidly with the water produced by melting snow and precipitation in early spring. Their life-span is only 60-70 days, and can be divided into three continuous stages: vegetative growth period, co-exist period of vegetative growth and reproductive growth and reproductive growth period, and proportion of reproductive growth is great in whole life history. Their fruits become mature before the rigorous weather of summer. So they are typical ephemeral plant escaping from droughty. 2. In Heteracia szovitsii, the development of the anther wall follows the dicotyledon type. Tapetum is the secretory type. Primary sporogenous cells develop directly into secondary sporogenous cells. The cytokinesis of microspore mother cells is of the simultaneous type. The microspore tetrads are trahedral. The ovary is inferior,bicarpellary and single locule. The placenta is situated on the base of ovary. The mature ovules are anatropous, unitegmic, tenuinucellate. Nucellus cells depress on tetrasporic period. Endothelium is constituted of one layer of cells. The magspore tetrads are linear. Usually, the chalazal megaspore is functional. The development of emebryo sac is of the polygonum type. The type of fertilization is porogamy. The development of endosperm corresponds to nuclear type.3. We first reported that the plants of 2 spieces can yield three kinds of achenes. According to the morphological difference of achenes in one head, we classify the flowers into three types: peripheral florets, transitional florets and central florets. They differ significantly in number, length and width of petal and the length of stigmatic lobe. There is a decreasing trend from periphery to center of captitulum. There are significant differences in P/O value between the peripheral florets and central florets. The number of pollen on stigma is 1/3-1/5 of the number of pollen in one floret. The abortion rate of pollen is low, from 0.2% to 5%.The captitulums efflorescence from 8:00 to 11:30. The peripheral florets blossom 20-50 minutes ahead of central florets. There are not effective pollinators in Garhadiolus papposus. Heteracia szovitsii is entomophilous plant.The main pollinators are bees.Every captitulum is visited about 20 times one day.The climax of visitation comes up 8:30~9:00. 4. The reproductive allocation(RA) of two species are 52.83±2.95% and 55.24±2.95% respectively, and don't vary greatly between years and individuals. In Heteracia szovitsii, the fruit-set rate of peripheral florets, transitional florets and central florets in one captitulum is significantly different. From periphery to center of captitulum, fruit-set rate decreases gradually, but the number of every kind of achene increase. Heteracia szovitsii can yield 1232.60±741.36 achenes. The ratio of achenes without pappus to achenes with pappus is 6:5. In Garhadiolus papposus, fruit-set rate is of significant difference between peripheral florets and central florets. The latter is higher, and the quantity of central achene is greater too. Every plant can yield 648±618.06 achenes. The yield of fruits is mainly influenced by the size of plant, dry weight of leaves and the number of reproductive modular per plant in two spieces, and it is not correlative to reproductive allocation. 5. Three kinds of achenes in one head are obviously different in shape, size, dispersal structure, micromorpha of pericarp and ecological behavior. Periph...
Keywords/Search Tags:fruit polymorphism, ephemeral plant, Heteracia szovitsii Fisch. et Mey., Garhadiolus papposus Boiss, et Buhse., embryology, repeoductive ecology
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