varieties, the prussic acid is low and confined mostly to the peel.
Sweet varieties can safely be eaten raw or boiled. In the bitter
varieties, the prussic acid is of higher concentration and is dis-
tributed throughout the tubers, requiring processing to reduce
prussic acid content before they can be safely consumed.

 Cassava tuber formation starts at two months after planting.
With time, tubers continue to increase in size by deposition of large
amounts of starch. Very young tubers have less starch than older
tubers. However, when the tubers become much older, they tend
to become more fibrous and lignified and the starch contents tend
to decrease. It is therefore best to harvest cassava at a time when
tubers are just old enough to have stored sufficient starch, but
not old enough to have become woody or fibrous. The exact
time to harvest depends very much on the cultivar. Sweet cultivars
mature from 6-9 months, while the bitter varieties require 12-18
months to reach maturity.

 ECONOMIC USES

 As Human Food The presence of a poisonous substance in
the tubers of some varieties has been responsible for its slow
acceptance as a food crop. However, world demand for more food,
combined with the development of processing techniques and


 better understanding of the nature of the cassava have helped to
 create the growing economic importance of the cassava as a food
 crop. According to John Onueme in his book, "The Tropical
 Tuber Crops," in many places in the tropics cassava has started to
 replace the more expensive sources of food calories like yams,
 taro, and sweet potatoes which were firmly entrenched in agri-
 culture prior to the advent of the cassava.

 Cassava tuber has a strong energy food value because of the
 high content of carbohydrates. Its vitamin C content is relatively
 more than that of other major root crops. A comparison of the
 food composition of cassava with other crops is shown in Table 1.

 The nutritive value of cassava tubers is comparable with
 crops such as yams, sweet potatoes, Irish potatoes, and taro except
 for the lower protein content of the cassava. It should therefore
 be realized that cassava, just like many other starchy food products,
 is only a supplier of carbohydrates and nothing else. The leaves of
 the cassava however, which are also used for food, more than make
 up for the protein deficiency of the tuber. Fresh cassava leaves
 contain approximately 6% protein and can be used in stews.

 Tubers of sweet cassava varieties can be eaten boiled, steamed,
 or fried. In the West Indies, sweet cassava tubers are prepared for

kBLE 1


Food Composition of a Diet of 1,000 Grams For Each of Five Starchy Roots
Compared With the Estimated Nutritional Requirements for an Adult Male


 IRISH
UNIT POTATOES


 SWEET
POTATOES


MANIOC YAMS


 ADULT MALE
TARO REQUIREMENT


Food Energy
Water
Carbohydrates
Protein
Fat
Calcium
Iron
Vitamin A
Thiamine
Riboflavin
Niacin (Nicotinic acid)
Vitamin C


Calories
 9
 9
 9
 9
 mg.
 mg.
 IU
 mg.
 mg.
 mg.
 mg.


820
780
189
 20
 1.0
 80
 7
Traces
 1
 0.3
 14
 100


1,170
 700
 273
 13
 4
 340
 1
5,000
 1
 0.5


1,460
 625
 347
 12


1,050
 724
 241
 24


1,040
 725
 242
 19


 3 2 2
330 220 230


 7
Traces
 0.6
 0.3


 8
Traces
 0.9
 0.3


 11
Traces
 1.5
 0.3


6 5 9
30 100 50


Source: Tropical Roots "Green Bulletin No. 19, Germany"


bob eaton ") | -
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