18 MISC. PUBLICATION 650, U. S. DEPT. OF AGRICULTURE 
simplified. In Puerto Rico, Moore (25) found that harvesting costs 
amounted to 64 percent of total labor expenses involved in growing 2.3 
acres of derris on a heavy clay soil. Milsum and Georgi (23) report ~ 
that entire root systems of plants can easily be lifted with an Assam 
fork when they are grown on sandy soils. 
Climate, too, is obviously a factor in the economy of production. 
Where dry seasons are prolonged, plant roots penetrate the soil deeply, 
thereby making the digging of them more difficult. In the Amazon 
Valley climatic conditions promote shallow root development on the 
part of lonchocarpus. The manner in which the derris root system 
will develop under the same conditions is being studied both in Peru 
and Brazil. A root-development study, made at Mayagiiez, P. R. 
(24), showed that 81 percent of the derris roots were located in the top 
16 inches of the soil. 
Figure 11.—Treillised derris, root system exposed; Santa Ana, El Salvador. 
Derris is said to have been grown successfully at altitudes up to 
4,750 feet above sea level (1). In Puerto Rico the rate of develop- 
ment during the first year of growth is noticeably slower at 2,400 
feet than at sea level and at 1,400 feet (25). While there is some 
difference in custom among planters as to cultural techniques and also 
some hesitancy on the part of research workers to prescribe a hard- 
and-fast routine for farmers to follow in growing derris, there is 
general agreement that the plants, if they have developed normally, 
should be harvested between the ages of 18 and 27 months. Moore 
and Jones (27) have shown that the greatest amount of rotenone is 
stored in the roots of D. elliptica during flushes of growth. In a 
greenhouse experiment, plants that were forced to grow rapidly by 
