Objective To study the growth laws of test-tube seedlings of Tiepishihu（Dendrobium candidum）

and provide a scientific basis for the rational control technique of test-tube seedlings in different growth periods.Method The indexes of growth development

content of polysaccharide and soluble protein

and photosynthetic characteristics were detected by applying general method.Result The increase of the height and stem thickness of test-tube seedlings was the fastest 5 to 8 months after sowing.The tillering peak was observed on 6th and 11th month respectively

and rooting peak was observed on 5th

9th and 12th month respectively.The biomass accumulation rate of test-tube seedlings was the highest during 7th to 8th months and 10th to 12th months.The ratio of root to stem（R/T） was relative low and the proportion between average dry weight of a single seedling to the total dry weight accounted to 90.6%.The content of polysaccharide in test-tube seedlings was the highest（5.07%） on 11th month and then decreased gradually.The content of soluble protein was highest（211.28 mg/g） on 8th month and then decreased gradually and reached lowest（119.55 mg/g） on 12th month.The test-tube seedlings grew well from 6th to 11th months.The best time for the transplant of the test-tube seedlings was on 10th month according to the dynamic accumulation of dry matter

changes of polysaccharide and soluble protein

seedling vitality and cost.The change of chlorophyll content showed obviously a trend of decreasing at first

and then increasing and decreasing again

and the change of photosynthetic rate was the same as that of the chlorophyll content during the growth development of the test-tube seedlings.After 10 months the chlorophyll content began to degrade.The changes of light saturation point and maximum electron transport rate of the test-tube seedlings were stable relatively

and the latter reached the highest 26 μmol/（m2·s） on 9th and 10th month.On 12th month the light saturation point and maximum electron transport rate reached the lowest.Conclusion The germination rate and quality of the test-tube seedlings of Tiepishihu are influenced mostly by the ripeness of seed.The intensity of illumination of tissue culture room is 27 μmol/（m2·s）

so the lower illumination may be one of factors limiting the growth of test-tube seedlings.It is better for transplant 10 months after sowing.The ratio of a/b of chlorophyll is controlled through regulating the light quality ratio of red and blue light

which will be good to improving the growth development of the test-tube seedlings.