List of members of the society accompany v. 22, no. 9; v. 25, no. 5.

Origins, specificity, structure, and physiology; Evolution at the center of origin; Taxonomy of the cereal rust fungi; Specificity; The formae speciales; Race specificity and methods of study; Genetics of the pathogen: host association; Histology and molecular biology of host: parasite; Virulence frequency dynamics of cereal rust fungi; The rust fungus; Controlled infection by Puccinia graminis f.sp. tritici under artificial conditions; Developmental ultrastructure of hyphae and spores; Development and physical of teliospores; Obligate parasitism and axenic culture; The host parsite interface; The rusted host; Effects of rust on plant development in relation to the translocation of inorganic and organic solutes.

For the last eighteen years we have been deeply involved in a cooperative effort with our Latin American colleagues in genetics, biochemistry, physiology, and molecular biology. We have been in close contact with scientists in a number of centers and have helped to organize symposia, workshops, and so forth, in an effort to accelerate their development and make their substantial work known. These symposia in Latin America have been quite successful. The fifteenth will take place in Brasilia in 1977. At the request of colleagues, we are in the process of developing a similar series in Asia. The first very successful symposium was held in Calcutta in 1973. We were most pleased when Dr. Amir Muhammed, Vice Chancellor of the University of Agriculture, Lyallpur suggested that we hold a symposium on a topic of great importance to Pakistan, Genetic Control of Diversity in Plants, under the auspices of the University of Agriculture. It is our hope that this symposium will be followed by additional ones in Pakistan as well as in other countries in the Far East. Leadership is quickly developing in the hands of outstanding scientists in these countries, and we appreciate the opportunity to cooperate with them. We are especially grateful to the Natiohal Science Foundation for makingPL- 480 funds available which made this symposium possible.

In introducing ourselves it should be told that in our native Latvian language our name is written LesiJ;l. s. In most English publications, as in this work, the writing has been simplified to Lesins, and often only the first initial has been used. Our interest in Medicago was first aroused during 1936-38, while em ployed as teachers in the agricultural and home economics school at Be brene, Upper Zemgale, Latvia. Some plants of alfalfa (M. varia, M. media), locally called 'lucema', were found growing wild along roadsides in that area, though no alfalfa fields had been seen in the vicinity within the me mory of local farmers. Some roadside plants were dug out and transplanted to the garden, but their seedset was poor. During the next few years we paid only slight attention to alfalfa, the reason being that Latvia is a country with Atlantic climatic features (annual precipitation 600-700 mm; mild win ters for its 56°-58° N. Lat. , with January isotherms between -3° and -7° C; moderately warm summers, with July isotherms between 16° and 18° C), which together with its soils, mostly of acidic, podzolic type, is not well suited for alfalfa production. It was not until 1945 in Sweden that work on alfalfa came to the foreground, when the senbor author was assigned investi gations on alfalfa seed setting by Dr. Erik Akerberg, then director of the Swedish Seed Association branch station at ffituna.

Genetic variation in plant populations. Exploration. Evaluation problems. Conservation and storage. Documentation and information management. Genetic resources centres.

An "age" has passed in the 40 years since we first observed recovery from radiation damage in irradiated bacteria. During the early 1930s, we had been discussing the possibility of rapid changes after radiation exposure with Farring ton Daniels, Benjamin Duggar, John Curtis, and others at the University of Wisconsin. After working with living cells, we had concluded that organisms receiving massive insults must have a wide variety of repair mechanisms available for restoration of at least some of the essential properties of the cell. The problem was how to fmd and identify these recovery phenomena. At that time I was working on a problem considered to be of great importance-the existence of the so-called mitogenetic rays. Several hundred articles and a score of books had already appeared dealing with mitogenetic rays, a type of radiation that was thought to exist in the shorter ultraviolet region. Our search for mitogenetic rays necessitated the design of experiments of greatest sensitivity for the detection of ultraviolet. It was vital that conditions be kept as constant as possible during exposure. All the work was done at icewater temperature (3-5°C) during and after exposure. We knew that light was an important factor for cell recovery, so all our experiments were done in dim light, with the plated-out cells being covered with dark cloth. Our statements on the effect of visible light stimulated Kelner to search for "photoreactivation' (as it was later called).