Calcium supply to plant roots

Direct observations of the calcium-45 distribution around the roots of plants growing in soil showed a pattern in direct contrast to that predicted from calculations based on the calcium concentration of the soil solution, transpiration rates, and plant calcium content. Whereas calcium-45 accumulation at the root surface was predicted, depletion was observed. It is suggested that preferential water movement in larger pores may decrease the expected solution calcium accumulation at the root surface. However, autoradiographs may give no indication of soil solution concentration depletion or accumulation because of the relatively high level on the colloid surface. The nature and extent of the depletion indicates how profoundly the plant root alters its immediate environment in the soil.     

Three-dimensional orientation mapping in the transmission electron microscope

Over the past decade, efforts have been made to develop nondestructive techniques for three-dimensional (3D) grain-orientation mapping in crystalline materials. 3D x-ray diffraction microscopy and differential-aperture x-ray microscopy can now be used to generate 3D orientation maps with a spatial resolution of 200 nanometers (nm). We describe here a nondestructive technique that enables 3D orientation mapping in the transmission electron microscope of mono- and multiphase nanocrystalline materials with a spatial resolution reaching 1 nm. We demonstrate the technique by an experimental study of a nanocrystalline aluminum sample and use simulations to validate the principles involved.     

Replication of the RNA of Bacteriophage f2

Events occurring after infection of bacteria with wild-type and a temperature-sensitive mutant phage indicate that there are two enzymatic activities necessary to replicate phage RNA. One converts single strands into double strands, while the other uses double strands to svnthesize viral RNA. The mutant is deficient in the first activity, probably because the mutation is in the gene specifying the requisite enzyme. On the basis of these and other results, a model is presented for the replication of phage RNA.     

EVOLUTION AS IT APPEARS TO THE PALEONTOLOGIST

The following facts are those which are put forth through paleontological observation, for verification by others: 1. That many origins of new characters are through some internal action in heredity. 2. That many important adaptive characters arise determinately, definitely, but by extremely slow stages. 3. That degrees of similarity in such origins correspond with degrees of kinship. 4. That degrees of kinship also affect to a certain extent, but not absolutely the time of appearance, or the time of the origin, or the rate of evolution. 5. That such origins find expression not sponta. neously, or irrespective of conditions, or from purely internal mechanical causes, but through some entirely unknown and at present inconceivable relation to ontogeny (habit and use), to environment (external conditions), and to selection. 6. That if such origins do spring from internal hereditary principles, as they appear to do in many eases, slow origins (mutations of de Vries) may be simply due to the same law operating with a different velocity.