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CAKE SUGAR.A very sweet and pure cane is found in those districts where the averagetemperature is such that a longer period is taken to maturity, and wherea season cold enough to check the growth of the cane occurs; when thisarrest 'of growth happens, the energy of the cane is presumably directedtowards the elaboration of the material already formed, rather than to theformation of new substance; it is in the districts lying on the confines ofthe tropics that this phenomenon happens.Rainfall.—The amount of water essential to the best growth of thecane is discussed in the chapter on irrigation. Under natural conditions anexcessive rainfall results in a cane of low sugar content, a deficiency inrainfall resulting in a cane with much fibre. The optimum rainfall is,of course, directly correlated to the prevailing temperature, the soil evaporationincreasing with rise in temperature ; thus Stubbs, 6 referring to Louisianaconditions, gives an annual rainfall of about 60 inches as most advantageous,of which about 45 inches should fall in the wet or growing season, and about15 inches during the dry. Such an annual rainfall would be classed as asevere drought in Demerara, where a precipitation of about 100 inchesresults in the maximum crop; the rainy season there should commence in midDecember, and continue without prolonged intervals of drought to the end ofJuly, the earlier months of the year being dry enough to allow of thecultivation of the heavy clay soils. A heavy rain immediately before harvestis reflected in a diluted juice, the vessels which carry plant food being thenfull of water at the moment of cutting.Wind.—The chief effect of winds in regard to agriculture, whether ofthe cane or otherwise, is concerned with the removal of soil moisture; themore frequently the stratum of air over a soil is removed, the greater isthe soil evaporation. The point of the compass from which the wind blowsis of influence in this connection; a wind blowing from the sea to the landconveys air heavily charged with moisture, increasing the humidity of theatmosphere, and lessening the tendency to soil evaporation ; it is probably forthis reason that in Demerara surface evaporation from exposed shallow vesselsis small compared with what would be expected from temperature conditionsalone. The surface evaporation there is 35.12 inches, per annum, comparedwith 31.04 inches at Oxford, and 82.28 inches at Bombay. 7 In Demerara theprevailing winds are the North-east Trades, blowing directly from the Atlantic,with no intervening mountains to cause a deposit of water as rain. Maxwell 8in Hawaii found that 120 square inches of exposed area evaporated in 270 days33,480 grams. of water, the relative humidity being 79.5, and the averagetemperature 79.5; this is equivalent to an evaporation of 28.4 inches perannum. Under equal conditions, but with the water protected from the wind,20