In germinating pine seedlings, acid soluble nucleotides, initially rich in AMP, accumulated, and were increasingly dominated by ATP. By 7 days, when hypocotyls were green but still dependent on the female gametophyte, the percentage of adenine nucleotides declined as other nucleotides increased. At 11 days, when gametophytic reserves were depleted, and seedlings were exposed to32P- phosphoric acid, adenine nucleotides accounted for over 70% of the recovery of32P from the nucleotide fraction.In seedlings, total RNA per unit weight increased to the 6th day, then levelled off. Comparison of electrophoretic mobilities of pine RNA on 2.5% polyacrylamide gels with ribosomal RNA from other sources revealed the following main types based on estimated molecular weights: 1.3, 1.1, 0.7, and 0.56 × 106daltons, corresponding to 25S, 23S, 18S, and 16S, respectively. On 10% polyacrylamide gels, the mobility of low molecular weight pine RNA was similar to that of yeast tRNA. The 1.3 and 0.7 × 106dalton fractions, representing ribosomal RNA, contributed 60–90% of the total RNA. During germination, the ratio of 1.3 to 0.7 × 106RNA dropped from 2.4 to 1.7 and reciprocated the pattern for water content of the seedling.32P was incorporated mainly into the 25S and 18S RNA by 11-day-old seedlings, indicating that synthesis of ribosomes was a major event in growing seedlings. During germination, the synthesis of RNA corresponded to an increase of total RNA detected cytochemically and to an increase of new cytoplasm with more ribosomes, as observed previously with hypocotyl cells by electron microscopic procedures.