CLIMATIC REQUIREMENTS m 



~ 4.3 



upon habit of growth is needed. The same breed appears to chap. 

 differ in size and in time of maturity at different altitudes and U ' 

 latitudes. Hunt (i) concludes that in the United States, as a 

 general rule, a breed becomes one day later for each ten miles 

 south or north of a given latitude, if the altitude is the same. 

 This means that a variety which ripens two weeks before a 

 killing frost in a given locality would only barely ripen if 

 taken 140 miles away from the equator at the same altitude, 

 the date of the first killing frost remaining the same. 



He advocates that, in introducing new seed it should prefer- 

 ably be obtained from about the same latitude. Similarity of 

 latitude may be a sufficient guide on a vast and nearly level 

 plain like that of the Ohio valley ; but where the topography 

 varies as it does in South Africa, other factors than latitude 

 and altitude influence the climate, and we doubt whether (with 

 the present lack of knowledge of these controlling factors) 

 South African farmers can make much practical use of the 

 suggestion. A breed which matures in 90 days in Australia 

 may take 100 or 110 days in the Transvaal. It is very 

 noticeable that the same breed takes a longer or shorter time 

 to mature in different years, according to the " season " ; in a 

 time of drought, growth is checked and flowering and fruiting 

 are hastened, while in a rainy season, growth is continued much 

 longer. Even within the Transvaal, and during the same 

 season, the same breed, grown from the same lot of seed, is 

 reported as having varied considerably in time of maturing in 

 different districts. This is due partly, no doubt, to the con- 

 dition of the soil as regards moisture at time of planting ; in 

 an air-dry soil such as is found over large areas during a great 

 part of the spring, the seed does not germinate as quickly as 

 in a moist soil. Allowance must also be made for the personal 

 equation, different observers holding different views as to when 

 the ear could be considered " mature " or safe from frost ; lack 

 of purity in strains of the same breed may also be a factor. 



32. Acclimatization. — It. is said that when a recognized 

 breed has been grown for some time under diverse climatic 

 conditions, it not only changes considerably in stature and 

 time of maturity, but that these habits become more or less 

 fixed so that, when taken back to the old conditions, the plant 

 does not at once respond to the change. In this way different 



