120 Barberry and the Black Rust of Wheat. [May, 



Field Observations on the Disease — 



Spring Stage. — The disease appears on the under surface of 

 the leaves of the common barberry in the form of yellow or 

 orange-coloured swollen patches (Fig. A). These patches vary in 

 size and may be as much as half an inch in diameter, and when 

 examined by the aid of a hand lens are seen to consist of 

 numerous cups known as " cluster cups." During the year 

 1920 the cluster cups were first observed on the barberry in Pem- 

 brokeshire on the 8th May. and from that date they were 

 seen continuously until the end of August. On reaching maturity 

 a few weeks after the appearance of the spot the cluster cups 

 open and the contents (a very fine yellow powder) are easily 

 distributed by the wind. This powder consists of the spores* or 

 " seeds " of the fungus, which when blown on to wheat produce, 

 if conditions are favourable, the summer or " red " rust stage. 



Summer Stage. — The summer stage generally appears on 

 the wheat leaves and stems in the form of reddish -brown, elon- 

 gated spots, which give the wheat a rusty appearance. From its 

 abundance on the stems the disease is termed in America the black 

 stem-rust. These spots consist of masses of " summer spores "t 

 which help to spread the disease during summer. The first out- 

 break of the disease for the year 1920 was noted on the 27th 

 July on autumn sown wheat in Pembrokeshire. The second case 

 was found in Cardiganshire on the 28th July; it was a bad 

 attack, and apparently the disease had commenced much earlier 

 than the date of the visit. This view was confirmed by the 

 farmer, who stated that he had noticed the disease about the 

 first or second week in July. The summer-spore stage was also 

 seen on spring wheat " April Bearded " as late as the 13th 

 September. The time of appearance of the disease in all proba- 

 bility depends on (1) climatic conditions, (2) proximity of 

 barberry, and (3) state of maturity of the wheat. 



The Winter or Black Stage. — A winter stage gradually dis- 

 places the red summer stage. It appears on the surface of the 

 r.tem in the form of conspicuous black streaks, which consist of 

 the resting sporesj of the fungus (Fig. D). During the year 1920 

 this stage was observed as early as the 27th July, the same date 

 as the red stage, and it was here noted that the transition from 

 the red summer stage to the black stage had taken place com- 

 paratively quickly, probably within a fortnight's time. In other 



° The spores from the cluster cups or aecidia on barberry are called 

 aecidiospores. 



f The Summer spores on the wheat "are termed uredospores. 

 J The resting spores produced from the black stage on the wheat are 

 termed teleutosp >res. 



