74 



and the low cost of cultivation involved in the prolonged period 

 of growth, it is abundantly clear that the cost of increasing the 

 starch yield from 3i to 7 tons per acre is out of all proportion to 

 the value of the increased product. 



It would appear therefore, that the most economic production of 

 starch would be attained by the cultivation of such a variety as 

 'Blue Top' upon a biennial basis. 



For quick returns 'White Top' would be the better variety and 

 in starting a starch factory it would be advisable to grow half the 

 cassava area as an annual and half as a biennial crop. 



The variety ' Black Stick' has steadily improved during the 

 second year of growth and now holds second place in starch pro- 

 duction with the record percentage of 38.2 per cent, of starch in 

 the tubers and an indicated yield of nearly 7 tons starch per acre. 

 'Smalling,' although giving a bigger tonnage of tubers than 'Black 

 Stick' stands decidedly below that variety in starch yield. "Mai- 

 lings" comes fourth with a little less than 6 tons starch per acre, 

 while 'Long Leaf Blue Bud' that led at 15 months has not since 

 gained at all in yield of tubers and shows only a very small increase 

 in starch per acre as the result of the further 6 months' growth. 



Clearly, this is a variety that is at its best at 15 months, and 

 one that it would not pay to grow as a 21 months cassava in com- 

 petition with the other varieties. 



Percentage of starch in the tubers. — -At 12 months' ' Luana Sweet' 

 had the highest content of starch (35.2 per cent.), at 15 months,' 

 'Long Leaf Blue Bud' heads the list with 37.4 per cent., while at 

 12 months' growth this variety is very slightly inferior to 'Black 

 Stick,' which leads with 38.2 per cent, of starch in the tubers. 



The recorded maximum starch content for a Jamaican Cassava 

 is 39.1 per cent, for the variety 'White Smooth Bitter' grown by 

 the Hon. T. H. Sharp at Inverness in Clarendon in 1903. 



This variety as grown at Hope only attained a content of 35.5 

 per cent, of starch. 



These experiments emphasize the fact that Cassava varieties are 

 so variable in their yield under different conditions of soil and 

 locality that it is most desirable to carry out careful tests of a 

 selected series before the best varieties for any given place and 

 purpose can be correctly ascertained. 



Not only is there a great variation in the yield of tubers, but 

 also of starch content and period of growth. 



Conclusions. 



1. Under conditions obtaining at Hope and without irrigation a 

 yield of loi tons tubers at 12 months, of 15J tons at 15 months 

 and of nearly 22 tons tubers per acre at 21 months has been re- 

 corded. 



2. The indicated yield of starch per acre has risen from 3i 

 tons at 12 months to 5| tons at 1 5 months, and 7\ tons starch at 

 21 months' growth. 



3. This yield has been obtained at a cost of about £5 per acre 

 and it is abundantly clear that we can produce enormous crops of 



