lo June, 191 2.] Water Rcq^uircmeiits of Crops. 349 



found upon the apple, pear, &c. Small rusty red-coloured spots upon the 

 bark, the scale insect occupying the central position, are usually one of the 

 first indications of attack upon the apple, pear, peach, and cherry plum. 

 Description. — General colour, sooty black, with a yellowish-brown spot in 

 the centre; shape, round. If the bark directly beneath these red spots is 

 cut, it is generally a carmine shade down to the cambium. With badly in- 

 fested trees the bark has a scurfy appearance, occasionally being pitted. 

 This pest does not confine its attack to fruiting trees, but has 

 a liking also for the hawthorn, &c. Treatment. — As there have 

 been several outbreaks of this pest in different parts of the 

 State, all buds or scions secured from an orchard should be 

 thoroughly examined, particularly about and behind the buds, 

 with a pocket magnifier. If there are any suspicious signs of attack or 

 scale insects to be seen, destroy by burning. Trees or stocks badly infested 

 should at once be destroyed by burning. If the trees are vegetative, spray 

 thoroughly with kerosene emulsion, strength r in 10. Follow up with fur- 

 ther applications at not more than ten days intervals. Further, treat in 

 late autumn and the winter months with red oil or crude petroleum oil emul- 

 sion. Strength, red oil. i in 30; crude petroleum, i in 25. No trees 

 should' be sent out of the nursery until examined bv some person who has 

 an expert knowledge of this disea.se. 



To he contimicd. 



WATER RECn IKEMENTS OF CROPS. 



By Jo/ni ir. Patcrson, B.Sc.. Ph.D., Exfcriiiu iitalist. 



Of the various requirements for the growth of a crop the most obvious 

 is a sutificient supply of water. Ordinary experience points to the con- 

 clusion that the quantity required must be large. Green-house plants 

 require frequent watering or they shrivel and dry up. A crop of 

 lucerne cut in the morning is soon withered, because it ceases to receive 

 water from the roots. Year after year the yields from dry farming depend 

 more upon rainfall than, practically speaking, upon anything else. In the 

 drier wheat areas of Victoria the soil may not receive enough rainfall to 

 grow a crop everv year, but, by fallowing in alternate vears the water 

 mav suflficiently accumulate to grow a crop every second. 



To determine exactly how much water is required by growing crops, 

 attemqjts have been made by different investigators in different countries of 

 the world. In all such investigations, apart from those of botanical interest 

 only, the method is the same. The amount of water evaporated or 

 "transpired" by a crop during its entire growth is found by weighing. 

 At harvest, the crop is cut off close to the ground and dried. When the 

 weight of water transpired is now divided by the weight of crop, there 

 is found what is called the ' ' transpiration ratio. ' ' This gives the number 

 of pounds (parts) of water transpired by the crop during growth for each 

 pound (part) of drv matter produced. 



In such investigations the water transpired is found by growing the 

 plants in pots. A pot is filled with a certain standard weight of soil 

 (usually from 20 to 120 lbs.) of a certain wetness, and the crop is planted 

 or sown. The pot is watered, usually daily, or four times a week ; and 



