This work will not deal with the. effect of irradiat onbut ony 4 ° epproved. with naturally ocourringmutations Anan. ‘Longevity studies.~Some’ of ‘the‘mice‘ecrviting Operatich ‘Greenhouse “are to be returned to the United States for observations over Ehe rest of their life span. ‘This work will be done in the Biology Divisipbn at ORNL. The Biology Branch was represented by Dr. Zelle at the Decembe 18 conference at Oak Ridge to discuss specific plans for the cataract, mor inci-+ dence, and longevitystudies of these mice. The overall size fof the study was reduced, a better statistical design developed espegially for the control mice, and a convenient system of recording data of one IBM card outlined at the conference. Personnel requirements, fingncing, and other problems pertaining to the program were discussed. The studies on the longevity of the mice from Greenhougke comprise only one part of a program on the effects of radiation on lonPevity. Other studies using external sources of radiation will be iniRiated with dogs and other species. Animals will be exposed to single X-ray treatments at various dosage levels, and also’ to intermittent expdsures. Irradiation effects on plants. Research at the U. S.Mepartment of Agriculture at Beltsville on an AEC project has dealt ext@nsively with the effect of radioactive isotopes on plant growth. In meastring the immediate effect of irradiation on plants it has been possiblfe to measure a decrease in root length, in top growth, and the size of nef leaves. These methods are only qualitative and with them little visibie injury to Plants is noticeable in such plants as barley and aifaitfa when the plants are prown in nutrient solutions containing less than 50 micypcuries of p3e per liter. It has recently been observed that cell division ceages in the meristematic region such as the root tip or stem tip when sfbjected to a constant relatively high level -of irradiation. The cells of the growing points enlarge; the cytoplasm in the cells become less dens#; the cell walls thicken. In short, the region takes on a somewhat abhormally mature appearance. The other growing regions of stems and roots afFe similarly affected by radiation. However, the cell's apical meristenb appear to be damaged when’ the plants are grown in solutions whose specific activity level was low enough to afford normal development of the rdst of the plant. By measuring the size of the peripheral apical meristematid cells under a microscope it has been possible to observe effects of irradiation from 50 microcuries of p3e¢: per liter of nutrient soiution down fo jess than 2 microcuries. This is a range of activity over which thereJis ro apparent change in the size of the plant. These resuits indicated that this method will servefas a quantita- tive measurement of the effect of irradiation on plants atf relatively low activities. It has thus been possiblie to show that eveu at the Lower redietion a ee jJevals there Sh is an faa affert Sa =e on plant oreonrthk: - 13- oe] ARCHIVES.