The detailed transmission electron microscopy observations of the immature carbon nanotubes (CNTs),obtained at relatively low temperatures by floating chemical vapor deposition (CVD), indicate that they can be viewed as intermediate objects and record rich and convincible traces about CNT evolution.The results clearly show that the CNT formation in floating CVD follows the particle- wire- tube stepwise evolution mechanism and also provide detailed information about the particle coalescence and structural integration and extension.This new knowledge not only gives a clearer picture for the CNT evolution in floating CVD but also might provide a general method for mechanism studies for other synthesis processes.