Vol. IX. No. 204. 



THE AGRICULTUKAL NEWS. 



61 



STUDENTS' CORNER. 



FEBRUARY. 



FiiisT Period. 



Seasonal Notes. 



On cacao estates, the produee of the early pickings will 

 have completed the process of curing. Samples of cacao 

 .should be taken at diflferent stages of this, with the 

 view of observing, as far as possible, the changes which it 

 undergoes successively. As the result of many investigation.s, 

 it is generally agreed that the (juality of the product is more 

 dependent upon that of the beans employed than on any 

 circumstance of the curing. In any case, cacao is improved 

 by fermentation, and this is generally practised, comparativel}" 

 little cacao that has been merely dried being in demand. 

 Note that the chief objects of the curing are to cause changes 

 in the puli> which will enable the cacao to be kept without 

 deterioration; to cause it to acijuire a flavour; and to give the 

 beans a good 'break'. What is the use of the last-named 

 quality t Two explanations are sometimes given as to what 

 really takes place, that is of importance, when cacao is 

 fermented. In one, this is held to be the termination of the 

 life of the bean; in the other, it is said to be ' malting', that 

 is the partial germination of the .seed, which is -sub.sequently 

 stopped by the rise i>f temperature. Neither of these seems 

 to be correct, for the first may be effected by mere drying, 

 when the characteristic properties consequent on fermentation 

 are never obtained; while, in the case of the latter, a good 

 product may be procured in the absence of any germination 

 whatever. In fermentation, as a matter of fact, the most 

 important circumstance .seems to be that absorption takes 

 place through the testa, while the latter remains intact; any 

 rupture of the testa is likely to result in the admission of 

 fungi, with a con.sequent deterioration in the value of the 

 product. What methods are in vogue for drying cacao ! 

 Describe any form of apparatus, that you may know of, 

 which is used for ettecting this. What is meant by 'claying' 

 cacao! Are there any advantages that are possessed by 

 clayed cacao which are not found in the ca.se of cacao that 

 has not been so treated! In both fermentation and drying, 

 extreme cleanliness should be observed. What is the chief 

 reason for this? In the preparation of cacao, what is the 

 jiurpose of trampling! Take note of the way in which the 

 product is packed for shipment. 



In the case of lime trees, discuss the advisability of prun- 

 ing. All dead wood that has been removed .should be burnt. 

 Why is this! What tissues are most active in healing wounds in 

 the stems of trees! Particular care should be exercised in 

 order to make sure that all cut surfaces have been tarred, or 

 covered with some similar antiseptic substance. Resin oil has 

 been suggested for the purpose: where this is used, it should 

 be mixed with an amount of tar or lamp-black sufficient to 

 make it show a distinct dark colour when spread over 

 a surface: otherwise, it will be ditfieidt to distinguish between 

 the treated and the untreated wounds, and some may be 

 neglected as a result. What is the object of the application 

 of such substances to cut surfaces! 



For what puri>oses may pruning be employed! Describe 

 carefully how a large branch should be removed from a tree. 

 Why should care be taken to avoid any tearing of the bark! 

 Where, in relation to the main stem, should the cut be made, 

 and why! What are the advantages of making it straight 

 across the branch, instead of in an oblique direction! Care- 

 fully ascertain what are the etl'ects of pruning upon the part 

 of the plant which remains. (See Pamphlet No. 52 of the 

 Department Series.) 



At present, the root borer of the sugar-cane is attracting 

 a certain amount of .special attention. Study the life-history 

 ot^ this pest, and ascertain exactly in what way it does injury. 

 What other plants is it known to attack, and what impor- 

 tance has this consideration in the matter of the rotation of 

 crops ! Distinguish between this pest and the weevil borer, 

 and consider the life-history of the latter in a similar way to 

 that given above for the root borer. Itemeiiiber, however, 

 that in doing all thi.s, where the insects exi.st, careful observa- 

 tions in the field are necessary, and may result in the 

 discovery of useful and important facts. 



Questions for Candidates. 



I'KEI.l.MINAKV <;UKST10NS. 



(1) l!y what agencies, natural aud artificial, is the 

 nitrogen of the air made available for plants as food! 



(2) What advantages and disadvantages are likely to 

 result from allowing lime trees to become covered with the 

 Bengal bean ! 



(3) How is lime applied to the soil! What are the usual 

 circumstances and uses of such application! 



INTERMEDI.\TE (JUESTIONS. 



(1) Give a method of eradicating a dangerous weed, 

 such as 'Devil's grass', from cotton fields. 



(2) !Nfention, broadly, the composition of the juice of 

 the ripe sugar-cane. How does that from the unripe cane 

 chiefly dirt'er from this! 



(3) How is the nitrogen in sulphate of ammonia con- 

 verted into nitrate nitrogen, in the soil! 



THE PASSAGE OF HEAT THROUGH 



SOILS. 



The following are some of the conclusion.s reached 

 in regard to this subject, in Bulletin No. ,59 of the 

 Bureau of soils, United States Department of Agri- 

 culture: — 



The transfer of heat from one soil particle to another is 

 influenced by the fluid filling the space between them, and of 

 course, this transfer is more easily effected when the fluid is 

 a good conductor of heat. In addition to the heat conduc- 

 tivity of the fluid, another factor has to be considered, that is 

 the resistance to the heat transfer which is found at the 

 boundary between the substances in contact. This ' transfer 

 resistance', or its reciprocal, 'transfer conductivity', is of suffi- 

 cient magnitude to enter into thermal calculations. If the 

 fiuid be in motion, there will be developed a resistance to 

 the transfer of heat, which has been shown to vary approxi- 

 mately with the square root of the velocity of the fluid. 



Heat will pass from a grain of soil to soil water one 

 hundred and fifty times more easily than from a grain of soil 

 to soil atmosphere. This comparLson seems to point out one 

 reason why an air-dry soil shows such a low heat conduc- 

 tivity. The rapid circulation of the soil atmosphere as eddy 

 currents within the minute .spaces between the soil grain 

 would, however, decrease the transfer resistance very greatly. 

 Such eddy currents are inevitably set up, as the hot soil 

 atmosphere on one side of a soil cavity expands and moves 

 up, and is replaced by the colder gases. 



The increase in heat conductivity of a soil produce<l by 

 wetting it is thus entirely due to the better contact between 

 the soil grains thus produced, since the soil material has, in 

 continuous massive condition, a much higher heat conductivity 

 than water. 



A soil conducts heat best and most quickly with a moist- 

 ure content near that recognized as the optimum. 



