64 3Iendelian Inheritance and YeUoiv Rust in Wheat 



observations could be made in 1918, and partly to see whether any 



difference in respect of the severity of attack would occur on the more 

 advanced and less advanced plants respectively. A portion of the prain 

 from the F^ plants was saved for sowinj; in successive seasons, and in 

 this way 7^, generations from the same hybrids were raised in HUB, 

 1919 and 1920. 



(2) TlIK 7'^ CENKRATION, 1918. 



(A) Climalic conditionn in 1918. 



Monthly records of the rainfall, etc., during the growing season are 

 given in Table I. The following brief description is taken from daily 

 observations, and will serve to indicate the general character of the 

 season. 



The month of April was very wet, with a high average percentage 

 of atmospheric humidity, and less than the normal amount of sunshine. 

 During May the weather was normal, and the wheats made steady 

 progress. May 3rd to 22nd was a warm period during which some heavy 

 showers fell; this period ended with a thunderstorm and heavy rain 

 on the 23rd. This was foIlf)\ved by a fine warm period which lasted until 

 June 17th. By this date the plants were beginning to need rain, but they 

 had not been checked in any way. 



From June 18th to 2r)th the weather was for tlie most part cool and 

 wet. Warm weather followed from June 26th to July 8th, and then came 

 a period of dull, mild, wet weather which lasted until .Inly 28th. 

 July 29th to August Kith was a tine, warm period. 



It will be seen that tlie season was divided into several comparatively 

 short alternating periods of fine and wet weather. This led to a steady 

 and normal growth of the plants and they were harvested in good con- 

 dition during the last-mentioned period. 



(B) Spread of rust during 1918. 



Pustules of Yellow Rust were first seen on April 8th, and by May 18th 

 its spread had become general: but the intensity of its attack was still 

 of a slight nature. It continued to spread very gradually until the end 

 of May, but so slow was its progress that at this date it was feared the 

 season might prove unsuitable for reliable statistics to be taken of the 

 F^ crop. Towards the end of May, however, it began to spread very 

 rapidly, and by June 21st this rust was very prevalent throughout the 

 cages. By the last-mentioned date th<! foliage of the more susceptible 

 plants was clothed with pustules. 



