176 SECTIONAL ADDRESSES 
Other cereal rusts, e.g. Puccinia glumarum and P. triticina, are widespread 
in Britain in certain seasons. Both these fungi over-winter in England 
in the uredospore condition, sometimes undergoing prolonged incubation 
in the host during low temperatures, although more precise information 
is needed with regard to the duration of such incubation periods. Alter- 
nate hosts appear to play no part in the recurrence of P. triticina and 
P. glumarum in this country, and in fact no alternate host for the latter is 
known. 
Much attention has recently been paid to the elucidation of the environ- 
mental conditions which promote epidemic outbreaks of potato Blight 
(Phytophthora infestans) and the Downy Mildew of the vine (Plasmopara 
viticola). By careful study of weather conditions warning can now be 
given in some countries as to the appropriate times for spraying these 
crops with protective fungicides. 
The storage rots of citrus fruits, bananas and apples have now been 
intensively studied, and some interesting correlations have been traced 
between the distribution of the causative fungi in the plantations, including 
the prevalence of their spores in the air, and the rots which subsequently 
develop ; this has been the subject of special investigation in apples by 
Horne !2 and Carter. In this connection a somewhat similar occurrence 
in another mycological field may be mentioned. Mould growths occa- 
sionally develop on meat kept in cold storage for long periods, rendering 
the meat unsightly. There is evidence that unhygienic conditions in the 
abattoirs promote these mould growths. Such fungi develop readily on 
plant debris and animal excreta, so that if the air surrounding the carcases 
is heavily laden with spores the meat will become dusted with them. The 
spores subsequently germinate and produce unsightly growths unless 
appropriately low temperatures are constantly maintained. 
In no branch of mycology has there been greater activity during the 
last decade than in the determination of physiologic or biologic forms 
of parasitic fungi, especially the Rusts and the Powdery Mildews. In 
general, these physiologic forms cannot be differentiated by morpho- 
logical criteria, but only by their host relationships. In Puccinia graminis 
for instance more than one hundred clearly defined forms have been 
identified on wheat alone. The plant pathologist has now to visualise 
therefore the occurrence, within many species of fungi, of large complexes 
of forms which differ in their parasitic proclivities, and thereby the task 
of the plant breeder in producing resistant varieties of cultivated plants is 
sometimes greatly complicated. In the determination of these physiologic 
forms of parasitic fungi their reactions on a range of differential host 
varieties are studied under known environmental conditions. In work 
of this kind it is essential that the host varieties should be genetically pure 
and that the inoculation tests should be carried out on plants at the same 
stage of development within precise limits of temperature, light, humidity 
and mineral nutrition, for variations in these respects may cause profound 
disturbances in the infection picture. 
12 Rep. Food Investigation Board, 1932, p. 285. Proc. Roy. Soc., B, 117, p. 154 
(1935). 
18 Trans. Brit. Myc. Soc., 19, p. 145 (1935). 
