29 
but the necessity for further investigations along these lines is 
evident to any one who takes up the problem of developing disease- 
resistant varieties. 
There are many well-known cases where a parasite introduced 
into a new region has caused serious injury to the native plants. 
One of the most noted cases occurred upon the introduction of the 
chestnut-blight fungus into the United States. This destructive 
disease was first observed in the parks of New York City, in- 
cluding Prospect Park adjacent to the Botanic Garden. Our 
native chestnut proved to be especially susceptible, and as a re- 
sult it is fast disappearing from our forests. On the other hand 
the chestnuts in the regions where the parasite was native appear 
to have developed a high degree of resistance. A somewhat similar 
situation arises when a host is introduced into a new environ- 
ment. Apple trees in Europe are not particularly injured by 
rust. When they were introduced into the United States, the 
native American cedar-apple rust-fungus severely attacked the 
introduced varieties, and has created a practical problem in 
apple culture in certain localities. 
During the past year the investigations in plant pathology at 
the Garden have been concerned with certain phases of this large 
problem of disease resistance. The investigations with the cov- 
ered smut (Ustilago levis) and loose smut (U. Avenae) of oats 
have been continued. A number of varieties of oats have been 
futher tested for their resistance to these two smuts. The most 
interesting results were obtained with some varieties which were 
received from Wales. This collection of varieties included 
several belonging to Avena strigosa. These have differed in im- 
portant respects from the strains of 4. strigosa which had been 
tested in previous years. Some of the strains from Wales have 
proved to be highly susceptible to both species of smut. 
An extensive series of experiments on the influence of tempera- 
ture and moisture on the infection of two varieties of oats, dvena 
sativa variety Victor and A. nuda variety imermis, by Ustilago 
levis was carried out. Some very interesting and definite re- 
sults were obtained. It was found that infection in both varie- 
ties occurred over a wide range of temperatures from 5° C. to 
30° C. The highest percentages of infection were obtained at 
