The discussion of high reserves of organic matter and N in Puerto Rican soils involves a study of the influence of elevation, rainfall, and temp. The 3 factors are interrelated to such an extent that little positive evidence can be obtained. The general trend is a lowering of the organic matter and N content with increasing temp. and decreasing rain. The high reserves of organic matter and N in cultivated soils is probably due to deep distr., and long-lived crops such as sugar cane, coffee, protected woodlands, and close-growing forage crops. The role of legumes is important in coffee groves and native pastures. However, legumes are not numerous in virgin forests. The rapid build-up of organic matter in exposed subsoil is probably due to the rapid growth of vegetation. Tropical kudzu, molasses grass and Merker grass are particularly effective. The frost-free boundary is suggested as a climatic limit for the original concept of Jenny regarding the progressive decline of soil organic matter with increasing avg. temp. The authors'' idea is that microbial activity and leaching can only deplete the soil if vegetative growth is stopped during a frost season. Puerto Rican soils are as high in organic matter and N as are many of the best soils of the temperate region. This high organic matter reserve of Puerto Rican soils is thought to be the reason for the relatively strong resistance to forces of deterioration.