154 Transactions british Mycological Soctety. 
5. [THE YELLOW RUST (PUCCINLA GLUMARUM Erikss. and Henn.). 
(a) Incidence. 
This rust is usually the earliest to appear and was noticed in 
the year 1921 as early as the third week of January on winter 
wheat at the University farm. It can be easily distinguished 
from either of the other two rusts by the orange-yellow colour 
of its uredo-sori, which are always arranged in long rows. 
As regards its incidence, there is absolutely no similarity 
between the data recorded for the two seasons under report as 
the following account will show. 
(I920-21.) The uredo-stage was very common in October on 
self-sown wheat on a small plot just outside the cages at the 
University farm. The plot was ploughed early in November 
but there was plenty of the rust on self-sown plants on some of 
the beds inside the cages also. During December and the earlier 
part of January 1g2I it was very rare and was found only as 
old pustules on withered leaves. On the 20th of January strips 
of fresh pustules were noted on several leaves of the winter 
wheat crop in cages sown in October 5-7th 1920. Since then 
the rust was seen spreading rapidly and took an epidemic form 
by the middle of March. Towards the latter half of July when 
the weather was exceedingly warm fresh pustules were rather 
rare. The harvest was reaped by the end of July. 
(I921-22.) In the month of August the rust was very rare 
on self-sown wheat or barley. During September and October 
too it was practically absent and no trace was found of it round 
Cambridge (in spite of a very thorough and daily search) except 
four or five self-sown plants on the 25th of October. It may be 
pointed out that during this period the brown rusts of wheat 
and rye (P. dispersa) and the dwarf rust of barley (P. simplex) 
were fairly common. From the 25th of October up to the end 
of May (1922), a period of over seven months, no trace of this 
rust was seen in this locality. It was first noticed in the be- 
ginning of June, but in spite of very favourable weather up to 
the harvest time the attack was an exceptionally mild one. 
