150 TROPICAL AGRICULTURE 



common species, the bitter cassava (Manihot utilissima) and 

 sweet cassava (M. aipi). These plants are native of South 

 America but are now grown throughout the tropical and sub- 

 tropical world. The plants attain a height of 6 to 8 feet and 

 bear palmately divided leaves, with 7 divisions in the bitter 

 cassava and 5 divisions in the sweet cassava. The bitter cas- 

 sava is more widely used in the Tropics than is the sweet cas- 

 sava. All varieties of both species may contain prussic acid 

 but the bitter cassava contains the highest percentage of this 

 poison. The prussic acid in cassava is located just under the 

 bark of the roots and is easily removed in the preparation of 

 starch and tapioca from these roots. Cassava is an important 

 human food product, being used by the natives of India and 

 other tropical countries like sweet potatoes and is also exten- 

 sively employed as a stock food. 



Cassava is commonly propagated by stem cuttings. The ma- 

 ture stems are cut into sections 8 to 10 inches long and partly 

 buried in the soil, being inserted commonly in a slanting direc- 

 tion at regular intervals in rows. The root or rhizomes are 

 ready for harvest 7 to 12 months after planting. The cut- 

 tings are commonly planted in rows 4 feet apart and about 16 

 inches in the row. In Florida, where considerable attention 

 has been given to cassava, the yield is about 6^2 tons of roots 

 per acre but exceptional yields of 10 to 12 tons have been ob- 

 tained. The yields in tropical countries are, as a rule, higher 

 than those obtained in Florida. The roots of a single plant 

 sometimes weigh from 25 to 5 pounds. These roots vary 

 greatly in shape, growing sometimes in the form of long strands 

 2 or 3 inches in diameter, and at other times in the form of 

 huge conical thickened masses. 



Cassava is used for a number of purposes. The milky juice 

 of the roots is concentrated by boiling into a thick sauce which 

 is used, after seasoning, by the natives of Guiana under the 

 name "cassaree" as a sauce or for preserving meat. The 

 tubers may be peeled and boiled or baked as food for man and 



