In cases where the new technology clearly is novel and sensible

 and when complementary inputs are available, extension can have a

 stunning impact. This seems particularly true with hybrid seeds.

 In one region of Kenya, hybrid maize was popularized in the mid-

 1960's. In 1965, 5,000 demonstration plots were set up, and 28 per-

 cent of the farmers visited one. Over 35 percentof farmers first heard

 about4hybrid maize from extension agents. (Almost 45 percent heard from

,friends or neighbors.) -Extension programs have had success with hybrid
 2 .3
maize in the U.S..,. and more recently with hybrid rice in China.

 Evaluation of extension programs is complicated by the fact

 that extension agents are not the only source of knowledge for

 farmers, and frequently they are only a marginal source. Farmers

 get information from friends and relatives, from skilled local

 farmers, from merchants and salesmen, etc. This information net-

 work, which might be called a "spontaneous extension system," is

 often very efficient in some social environments. Historically the

 diffusion of new crops around the world--including maize and potatoes

 from the Western Hemisphere to Europe and Asia, early maturing varieties

 of rice in Asia, numerous cash crops (sugar, indigo, opium, etc.)--has been

 quite rapid, and has not required formal extension services. Early


 John Gerhart, "The Diffusion of Hybrid Maize in Western
 Kenya," (Mexico. D.F.:CIMMYT, 1975), p. 9.

 Zvi Griliches, "Research Costs and Social Returns: Hybrid
 Corn and Related Innovations," Journal of Political Economy,
 October 1958.

 "Some Problems on the Development of Hybrid Rice," Scientia
 Agriculture Sinica, Feb., 1978. Available in JPRS 71, 717, PRC
 Agriculture no. 3., p. 1-18.

 4This phrase is suggested by Michel Cernea.
 V. W. Ruttan and Yujiro Hayami, "Technology Transfer and
 Agricultural Development, Technology and Culture 14:2 (April 1973),
 p. 120.