REPORT OF THE SECRETARY OF AGRICULTURE. 51 



tained in the fertilizer or otherwise added to the soil. The quantity 

 of magnesia required by the crop, however, is comparatively small — 

 perhaps not more than half that of the potash which is needed. 

 With constantly decreasing supplies of cottonseed meal and other 

 similar materials containing appreciable quantities of magnesium, 

 it is apparent that there will be greater necessity for making special 

 provision for magnesium in the fertilizer mixture. 



POSSIBIMTIES OF RUBBER PRODUCTION. 



On the basis of a special appropriation for this purpose, more 

 extensive investigations of rubber-producing plants are being under- 

 taken to determine the possibilities of producing rubber in the 

 United States or in adjacent tropical regions. The need of develop- 

 ing other sources of supply is shown by the rapidly increasing con- 

 sumption in the United States and the serious danger of supplies 

 from the East Indies being interrupted. About nine-tenths of the 

 world's supply of crude rubber now comes from the East Indian 

 plantations, while three-quarters of the total supply is used in the 

 United States. These two facts are a standing challenge to both 

 agricultural scientists and business men. 



In view of the large number of plants that are known to produce 

 rubber and of the wide range of diversity among such plants in 

 habits and conditions of growth, adequate determinations of cul- 

 tural requirements and possibilities are not to be expected until 

 many observations and experiments have been made. Facilities for 

 experimental work are being extended in the different regions where 

 rubber-producing plants can be grown, and expeditions are being 

 sent to foreign countries to study the habits of the plants under 

 native conditions and to secure the best stocks for propagation and 

 breeding purposes, so that vigorous, high-yielding strains may be 

 developed as the basis of production. 



Under the existing world conditions it is clearly desirable that a 

 thorough study of the potential rubber-producing plants of the 

 world be carried forward vigorously and without interruption, with 

 a view to ascertaining the most promising sources of increased sup- 

 plies of rubber to meet the increasing requirements of our industries 

 and of the users of rubber, who now constitute practically the entire 

 population of the country. 



