Xylem of sugar maple and yellow birch trees were exposed to natural infection by making axe blazes to simulate mechanical injuries. After 8, 21, and 34 months, dissection and isolations made from the discolored wood permitted the localization of certain microorganisms in three arbitrarily determined zones. Longitudinal and radial development of discoloration associated with wounds was more rapid in yellow birch than in sugar maple. There was evidence of a succession of organisms in the colonization of the wounds which was subsequent to the first discoloration process and involved different organisms in the two hosts. In general, decay fungi did not appear until after 21 months. Cytosporadecipiens occurred exclusively in discolored wood of sugar maple while Phialophora spp. and Cephalosporium sp. dominated the discolored wood of yellow birch. Bacteria were more frequent in yellow birch than in sugar maple. Relationships between size of injuries, linear extent of the discoloration produced, and identity of the various organisms involved are also presented.

The influence of light interruption of the dark period on flowering and certain growth characteristics of alfalfa (Medicago spp.) was studied under field conditions at Tucson, Ariz.One light interruption of 30 min in the middle of the dark period caused significant differences in flowering percentage, height, and dry‐weight production of specific cultivars. Alfalfa plants that were grown under light interruption had smaller crowns, flowered earlier and more profusely, and produced less dry matter compared to plants grown under natural daylength.Seasonal temperatures influenced the effects of light interruption of the dark period. Differences between light treatments with respect to flowering were most evident during shorter natural daylengths which coincided with the cooler growth periods, while differences in production of dry matter were most evident when maximum and minimum temperatures were highest.Light interruption of the dark period can be used to obtain more rapid and complete flowering of alfalfa under field conditions.