Abstract: Ultra-structure of outer and middle scales of bulbs of Lilium oriental hybrids cultivar‘Sorbonne’ were observed and analyzed systematically by using the transmission electron microscope (TEM) during the bulb development. The results indicated that there were a lot of big starch granules, proteins and
lipid droplets in the scale cells at the planting stage. The bulbs played the role of “source” at this stage. With the growth of lily plant, a great number of mitochondria appeared near the cell wall and around the starch grains. This indicated that catabolism was the predominant processes in scale cells. The number of starch granules, proteins and lipid droplets decreased and reached the minimum at the blooming stage. After blooming, the amount of starch granules, proteins and lipid droplets increased significantly, the bulb
converted to play the role of “sink” and started to accumulate a large number of assimilation products. There were full of starch granules and proteins in the scale cells at the harvest stage. At the same time a large
number of plasmodesmata were observed between cells of outer and middle scales, and many vesicles were also observed near plasmodesmata at the blooming stage, which indicated that symplastic pathway was the main pathway in the exchange and transportation of assimilates during the process of functiontransmission of source and sink of lily bulb.

Key words: lily, developmental phase, source-sink relationship, scale, ultra-structure