May, 1922] 



RAINES VEGETATIVE VIGOR OF THE HOST 

 Barley 



217 



third leaf. The rust increased steadily in abundance on the leaf blade 

 until it reached the maximum, and only then began to appear on the leaf 

 sheaths. On the stem there were never more than a few scattered pustules. 

 Teleutosori did not appear until the middle of September. They were to 

 be found only on plants of the two oldest plots, and then not without care- 

 ful search. The observations of October 23 showed a distinct drop in the 

 amount of rust on all the plots of wheat. The new leaf growth of October 

 tended to show but little rust. In view of Johnson's (1912) findings that 

 low temperatures promote uredospore germination, these observations 

 may be interpreted as indicating greater resistance to rust infection on the 

 part of the host tissue due to the decreased rate of metabolic activity con- 

 sequent on the onset of cooler weather. 



All of the plots of rye except that sown August 25 headed out, but the 

 rate of growth varied as is indicated by the successively greater intervals 

 required by the younger stands to head out. The behavior of the rust on 

 the plots of rye was much the same as on the wheat. In the younger 

 plantings it was somewhat less marked and less severe than on the wheat 

 plants of the same age, but the development of the rust was more severe 

 on the rye than on the wheat. It seemed, too, to go more readily to the 

 leaf sheaths and stems in the case of the rye. No teleuto was found on 

 the rye. 



Of the oats, the first three plots headed out in 77, 65, and 70 days 

 respectively; the fourth plot produced only one head, 91 days after planting. 

 The plots planted August 5 and August 25 never headed out. No rust 

 appeared on the oats until August 12 when four plots were up, ranging in 

 age from seedlings in the four-leaf stage to plants in bloom. The rust 

 appeared on all four of the plots at the same time and in relatively the 

 same abundance. However, once the rust had appeared, its subsequent 

 history on the various plots differed decidedly. The older the plant, the 

 greater the abundance of rust on it, and the larger proportion of the rust 

 in the teleuto stage. 



In the series of barleys, the three older plots headed in 42, 50, and 50 

 days respectively. The fourth put out a few heads 70 days after planting. 



