66 
he may discover that there are other races of funei about which 
nothing was known, and their discovery compels a new start. 
While these findings are of great importance with reference to 
cereal grains, they have a much wider significance. Physiologic 
races of plant pathogens are known among practically all groups 
of fungi—rusts, powdery mildews, downy mildews, smuts, ete. 
The knowledge of their existence and their capacity for infecting 
strains of cultivated plants is essential to successful breeding. 
Permanent, valuable results can only be obtained where they are 
fully recognized. 
It may be mentioned that highly important results along the 
line of breeding disease-resistant plants—cereals, vegetables, and 
ornamentals—have been obtained, and provide one of the most 
valuable methods for the control of various types of disease. 
The discoveries in the field of physiologic specialization, however, 
emphasize the fact that successful breeding for any character of 
such complexity as disease resistance is a continuing problem, 
The breeder who proceeds with a thorough background. of 
knowledge on the physiologic specialization and of the inheritance 
of disease resistance is most likely to succeed. 
Control of Iris Thrips 
Studies on methods of control of Iris thrips have been con- 
tinued during the year by Dr. L. Gordon Utter in collaboration 
with Dr. Floyd F. Smith, of the Bureau of entomology and Plant 
Quarantine, Washington, D.C. Thrips are a serious menace to 
the successful cultivation of Iris, and the City of New York (like 
many other cities) has tens of thousands of iris, planted in the 
parks and gardens and along the parkwavs of the City. To find 
an effective method of control of this troublesome pest is, there- 
fore, of prime importance in the proper maintenance of these 
beautiful plantings, as well as the collection of bearded and 
beardless Iris at the Botanic Garden. 
Exploration and Geographical Distribution 
Of special popular interest is the study in geographical dis- 
tribution, undertaken by Dr. Svenson in the early part of the 
year with the aid of a grant from the Guggenheim Foundation. 
