Abstract: Growth and net assimilation rate (NAR) were measured periodilly during the first year of growth of masson's pine seedlings grown in wooden boxes under field conditions. The main tesults obtained are as follows:1. Two distinct maxima of the NAR curve were shown in the annual growth of the seedlings. The first maximum appeared during the rapid growth stage of root system between May 1 and June 8; the second, during the rapid growth staye of stem and lateral roots between July 8 and August 7. NAR and roots growth were positively correlated.2. The vegetative organs showed differentes in growth rate in different seasons of the year. From May 11 to June 8, root growth was foster than height growth of the stem. From June 8 to August, stem growth exceeded that of the root. After August the growth rate of leaves, stem and tap root decreased to a low level, while that of the lateral roots increased.3. Before early August, much of photosynthetic products was utilized to form the root system and leaves. After that period photosynthetic products were mostly used for the growth and development of the lateral roots and stem.