The Biological Characters Of Snow Lotus(Saussurea Involucrata)

The biological characters of Snow lotus (S. involucrata (Kar. et Kir.) Sch. –Bip.) including the traits of habitats, vegetative developmental anatomy, embryology,reproductive characteritics and the growth traits of seedlings were studied by both the field observation and the experiment indoor in this paper. Meanwhile, the reasons which endanger this species were discussed. The main results were as follows:1. Snow lotus is a typical perennial, monocarpic, alpine plant. In Tianshan mountain, it usually lives in the extremely rigorous environment generally, in which there is lack of the soil. The climate of the habitats is variable companied with big wind, scarce oxygeon and strong ultraviolet, and the discrepancy of temperature between the day and night is high. The vertical stem is short with the dense rosette leaves during the vegetative growth,and elongates quickly to 15-40cm during the reproductive growth. There are many capitulums at the top of stem, with many bracts around these capitulums.2. In the primary structure of root, the primary xylem is diarch and the development of both the primary xylem and the primary phloem is exarch. During the developmental process from the primary structure to the secondary structure of root, the cells of cortex is active: the cortex cells close to the exodermis disintergrate and result in the formation of aerenchyma, and those next to the endodermis differentiates actively to produce a large number of the thin wall cells to contribute the secondary structure in root. The lateral root as well as the part of the vascular cambium develops from the pericycle. So the secondary growth of root results from the activity of both vascular cambium and parenchyma in the cortex. Meanwhile, the phellogen comes into being in the cortex under the epidermis. This mechanism is rare in other plants. The root-stem transition region and the root in the elder plant reproduce the abnormal secondary structure which is similar to the rode caused by separation of the vascular bundle. Moreover, the vascular bundles in stem and leaf are amphicribral and the cambium between the exogenous phloem and the xylem acts strongly. The stem is hollow with pith cavity. There is a great quantity of aerenchyma and secretory canals distributed in root, stem and leaf.3. The development of the anther wall follows the Dicotyledon type. Tapetum is the secretory type. The cytokinesis of the microspore mother cell is of the simultaneous type. The microspore tetrads are tetrahedral mostly. The mature pollen grain is the three-celled type. The ovary is bicarpellary and single locule. Each locule contains a single ovule. The placenta is situated at the base of ovary. The mature ovules are amphitropous, unitegmic, tenuinucellate. The megaspore tetrads are linear. Usually, the chalazal megaspore is functional. The development of the embryo sac is of the Polygonum type. The embryogeny conforms to the Astered type.The development of the endosperm complys with the Nuclear type. Antipodal embryo is existent in the Snow lotus. 4. The display pattern of the floral is particular. The average of day temperature inside the bracts is obviously higher than that outside the bracts. The higher temperature inside the bracts provides the development, pollination and fertilization of the capitulums with the optimal micro-environment. Furthermore, the pistil and the stamen grow at different speed at the flowering. The rapid elongation of the steman is prior to that of the pistle and the anther is congitudinal dehiscence inward. This special growth pattern of the pistil and the stamen makes the stigma receive the pollens efficiently. This phenomenon was reported rarely in Compositae. Furthermore, pollinator is rare, and the frequency of visits per head is very low, but the average fruit-set rate can arrive at 56.72% in the fertile captitulum. So we consider Snow lotus is characteristic of either the self-pollination or the facultative self-pollination. The discrepancy of growing speed in the pistil and the stamen may be a speci...