Barchan dunes are found where sand availability is low and wind direction quite constant. The two dimensional shear stress of the wind field and the sand movement by saltation and avalanches over a barchan dune are simulated. The model with one dimensional shear stress is extended including surface diffusion and lateral shear stress. The resulting final shape is compared to the results of the m...

Crosses between “franciscana sulfurea” and sulfur-dwarf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 Crosses between ‘ffranciscana sulfurea” and Oenothera franciscana ...................... 328 Chromosome configurations of the hybrids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 Interpretation of data.. . . . . . . . . . . . . . . . . ....

The researches of MORGAN on lethal factors, of BARTLETT on mass mutation, and of RENNER on empty seeds, have led me of late to the conception that lethal factors and hybrid mutants play a large part in the splitting phenomena which accompany the normal mutations of so many species of Oenothera. The question, which part of those phenomena may be explained by this view, has to be faced. The cross...