153 



rience shows that Cassava is very subject to this pest in the 

 Liguanea plain ; I have not observed it in other parts of the island. 



Experiments in spraying with paraffin-naphthalene emulsion 

 and liver of sulphur are to be tried at Hope, but it would appear 

 that the plant ultimately recovers from the attack of this pest and 

 the net result is only a prolongation of the period required for 

 full development of tubers. The starch content of the tubers was 

 quite satisfactory and most varieties were in a fit state for the use 

 of the starch manufacturer at the end of the first 12 months. 



The leading variety of the series is " White Top " with IO5 tons 

 tubers per acre containing 33 6^ of starch equal to 7,902 lbs. 

 starch per acre. This is a bitter variety yielding rough-coated 

 tubers of a dark colour and was obtained from the peasants of 

 St. Elizabeth by Mr. W. Cradwick. 



The variety that comes next is one called " Long Leaf, Blue 

 Bud " yielding 6,552 lbs. of starch per acre. This is a variety 

 with light brown tubers and white flesh which we obtained from 

 the Hon. T. H. Sharp and is largely grown by the peasantry in 

 the Inverness district of Clarendon. The highest percentage of 

 starch was found in " Silver Stick " also obtained through Mr. 

 Sharp from the same district; this contained 35 percent of starch. 



The variety " Brown Stick" which is well thought of in many 

 districts gave a poor yield at Hope, although the starch-content 

 was good. 



We have established the fact that the specific gravity of a Cas- 

 sava tuber bears a fairly close relation to the starch-content of the 

 tubers. With the Sweet Potato we found little variation in gravity 

 and many varieties containing a good deal of starch were of prac- 

 tically the same density as water. With the Cassava it is quite 

 different and we are preparing data from which it is hoped that a 

 factory will be able to estimate the starch-content of cassava 

 tubers by means of a Cassava Balance. 



By weighing 50 lbs. of tubers in air and again in water the loss 

 of weight represents the weight of a volume of water equal to that 

 of the tubers. The specific gravity of the tubers — at the tempera- 

 ture of observation — will then be the ratio of 50 lbs. to the loss in 

 weight recorded. 



A table is being constructed in which if 50 lbs. cassava tubers 

 are taken, the weight when immersed in water will be referred to 

 an approximate percentage of starch in the tubers. 



It is obvious that this factor would only be an approximate 

 guide to the starch-content, but its use should enable a factory to 

 pay for tubers a price based upon a presumptive content of starch. 



The tables set forth the appearance and habit of each variety 

 as determined by Mr. W. M. Cunningham of the Experiment 

 Station which may enable planters to identify local varieties 

 grown under a different name with those appearing in our list. 

 A description of the tubers and finally a table giving the yield of 

 tubers per acre, their composition and the total indicated starch 

 per acre from the 23 varieties are also appended. 



