376 REPORT OF THE CONFERENCE ON GENETICS. 
farmer. But rigid straws can be built up as readily as other undesirable 
characteristics can be eliminated, and neither of these features offers 
insuperable difficulties to the breeder of to-day. 
Some five seasons ago certain facts suggested that the liability to the 
attacks of this fungus pest was possibly a Mendelian character. ‘To test 
the matter, crosses were made between the most susceptible and the most 
immune varieties then available. They were not as suitable for this pur- 
pose as one could have wished, for the immune parent was far from being 
so in reality, though it was not nearly as susceptible as its fellow. The data 
obtained pointed in the right direction, and since then the experiment has 
been repeated and extended with far more suitable material. In these 
later experiments I hate been able to make use of a wheat which, though 
it has been under observation for four seasons, has remained free from 
rust in spite of the fact that it has always been grown in company with 
the most disease-susceptible varieties obtainable. Crossed with Michigan 
Bronze, a variety more prone to rust than any other, it gave a batch of 
hybrids on which it was difficult to find an area an eighth of an inch 
square unattacked by the fungus. Even the awns and grain were 
infected. On comparing these plants with the susceptible parent, there 
appeared to be no difference between them in this respect ; but whereas the 
parent hardly set a grain, the hybrids yielded a moderate crop, but one 
badly shrivelled by the attacks of the parasite. 
Every available grain was sown in plots alongside the parent varieties, 
part on land which had been partially exhausted by a previous crop of 
wheat, and part on land which had carried a crop of clover the previous 
season and consequently was in high condition. The difference in culti- 
vation, however, made no difference in the results of the experiment. 
The rust was late in appearing that season, but again every plant of the 
susceptible parent was stricken, and all of the immune type escaped 
entirely. The hybrid plots were badly attacked, and when the epidemic 
seemed to be well advanced the plants were sorted into two groups— 
namely, those which were attacked, and those showing no signs of disease 
even on the withering basal leaves. On some plots the diseased plants 
were cut out, leaving those free from infection for a subsequent examina- 
tion. A few individuals which had escaped the attack at the early stage 
became infected later, and these were then added to the total of susceptible 
plants. The statistics showed that 1,609 diseased plants were present, 
and 523 immune, or a ratio of 8:°07:1. There cannot, I believe, be any 
question that these latter were really immune, for they were surrounded by 
plants covered in rust, whose leaves were continually rubbing against 
them. Further, if a variety is susceptible, no plant of it under field con- 
ditions ever appears to escape. 
The two parents differ from one another in other characters besides 
the immunity and liability to the attacks of rust, and it may be noted 
that, as one would expect, individuals similar to the immune parent 
morphologically but susceptible to rust were found, and also the rust- 
proof form of the susceptible parent. 
Other experiments have been carried out on these lines, and though the 
statistics have still to be analysed, there is no doubt that they have given 
the same results. There are indications that other diseases besides yellow 
