Abstract1. The various methods used by Gómez (1) Lee (2) Lee and Bissinger (3), Nutman (4), (5), (6), Trench (7), Venkatraman (8), and Weaver and his associated (9), (10) for the study of the root system of plants have been described and discussed fully. 2. A new method developed by the writers has been described and used for the study of the root system of coffee, C. arabica L. in Puerto Rico. Briefly, this method consists in excavating the volume of soil assigned to each tree under study by blocks of one-cubic foot each and separating, drying and weighing the roots obtained from each block. By keeping an excavation map for the root system of the trees, the exact position of roots obtained for each block is obtained, therefore being possible to determine the quantity of roots present at the various soil levels excavated and the lateral spread of the roots as well. 3. Ninety-four percent of the coffee roots of all trees were found in the top-most 12 inches of soil. 4. The high percentage of organic matter in Coloso Clay, especially in the top-most layers, and the better aeration at the surface, apparently accounted to a great extent for the presence of more roots in the top-most 12 inches of soil. 5. The imperfect drainage conditions existing at localities where Coloso Clay predominates affect the development of the root systems of coffee plants. 6. Coloso Clay is a productive soil when proper drainage conditions are provided and the principal plant foods are generally distributed uniformly to a depth of 48 inches. 7. A heavy and vigorous coffee tree top is not dependent on an extensive root system. 8. There is no fixed "(tops to roots) ratio" in coffee trees, but generally the ratio of tops to roots may be figured to be 8:1. 9. In selecting trees with vigorous, heavy tops and a strong, extensive root systems, the diameter of the trunk is a better indication of the possession of these characteristics than either the height or the lateral spread of the tree. 10. There was approximately 50 percent of water in the upright stems of coffee trees, 23 percent in the lateral branches and leaves, 39 percent in the whole tree tops and 50 percent in the roots. 11. The absorbing area of the root system is not confined to definite places on the soil but is distributed thru-out all places penetrated by the main and secondary roots. 12. The vertical penetration of roots of 7-year-old trees is 3 feet and the lateral extension is 4 feet. 13. The results obtained have been discussed fully in relation to possible aplications in the performance of agricultural practices followed by farmers in coffee plantations.
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