S. F. Armstrong 67 



(3) The F, cultures. 1919. 



Since it was impossible to deal with sufficiently large F^ cultures 

 raised from all the Fn plants, a number of the latter were chosen so as to 

 include individuals showing every grade of attack, as well as a number 

 of those that had remained rust-free. Altogether 198 F.^ plants were 

 taken, and the grain sown in tiie autumn of 1918. 



(A) Climatic rondi/io)}f:, nidiuiring, avd qrnuih nf Ihr niltiirex in 1919. 



Monthly records of the weather are given in Table T. The season 

 proved a most trying one for the plants, there being three prolonged 

 periods of extreme chmatic conditions. 



The fir.st of these was from January IStJi to February 13th, during 

 which the ground was frozen and snow-covered. So unfavourable was 

 the spring weather that as late as the beginning of May the cultures 

 were still in a very backward condition. Before they had sufficient time 

 to recover they were faced by a period of drought which lasted from 

 May 13th until June 19th. Throughout this period of 38 days the average 

 daily sunshine was 10-1 hours, but the total rainfall only 6-2 mm. Indeed 

 the total fall of rain from May 1st until June 19th amounted to onlv 

 8-9 mm., i.e. 0-35 inch during .50 days. 



On May 27th a top-dressing of nitrate of soda was apphed to all the 

 cultures, at the rate of 4 cwt. per acre. It was hoped that this heavy 

 apphcation would counteract the drought effects to some extent as soon 

 as rain fell. However, rain did not fall in sufficient cjuantitv to carrv tlie 

 nitrate into the soil until 23 days later. By June i7th it appeared prob- 

 able that most of the cultures would be ruined, as many of the plants 

 were in a critical condition and the basal foHage was dying off. Three 

 days later (June 20th) a heavy fall of rain carried the nitrate to the roots. 

 The change was sudden and most marked, for by June 23rd most of the 

 plants showed a notable recovery, and soon afterwards they began to 

 send up numerous side tillers. 



The period of drought referred to was immediately followed by a 

 lengthy period of the very oppo.site conditions. From June 20th until 

 the end of July the weather was cool, dull, and moist. During this time 

 (42 days) 4-4 inches of rain fell, but the average daily sunshine was only 

 3-6 hours. One of the general effects of this weather — combined with the 

 action of the nitrate — was to delay greatly the ripening of the plants. 



