pp. 545-560. More general techniques are reviewed by L. P. Smith in Weather and Food, World Meteorological Organization, Geneva, 1962, pp. 37-60 (Freedom from Hunger Cam paign Basic Study No. 1). Practices used to prevent frost are outlined by Jen-Hu Chang in Climate and Agriculture: An Ecological Survey, Aldine, Chicago, 1968, pp. 100-108.

3. I have discussed this subject in considerable detail in Survey of Multiple Cropping in Less Developed Nations, U.S. Department of Agriculture, Foreign Economic Develop ment Service, FEDR-12, October 1971, 108 pp.

4. This may be particularly true if the earth continues a cooling process which has been underway since the 1940's. (See James D. Hays, "The Ice Age Cometh," Saturday Review of Science, April 1973, pp. 29-32; Bryan Silcock, "Ice Age to Come?" The Sunday Times (London), April 15, 1973, p. 17.)

5. For a more detailed discussion of the characteristics of the major plastic coverings, see, inter alia, J. A. Sondern, Plastic Films Used in Horticulture, Instituut voor Tuinbouwtechnick, Wageningen, Holland, September 1972, pp. 1-12.

6. The most advanced research units, involving both climate-controlled greenhouses and growth chambers, are known as phytotrons (see ch. Ill, fn. 120). Greenhouses are increasingly being used for experimental work in the developing nations. A phytotron is being erected at the International Rice Research Institute (Los Banos, Philippines) with the support of the Australian government.

7. Liberty Hyde Bailey, The Forcing Book; A Manual of the Cultivation of Vegetables in Glass Houses, Macmillan, New York, 1897, p. 1.

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