The structure of starch grains from wheat grown under constant conditions.

Abstract

This is a report upon the starch of the seed of Hard Federation wheat grown under continuous constant illumination by Mazda C lamps, the other external conditions such as temperature, humidity, water- and salt-content of the sand in the pots being kept as constant as possible. 1

The starchgrains did not show the lamellation or rings that can be seen in the starch of ordinary wheat seeds. This difference is all the more striking if the two kinds of starch are compared, after heating to a temperature at which the grains begin to swell, while their border is still refractive. Inside the swollen unlamellated grains, very refractive radial needles can be seen, attached to the refractive border of the grain or to the circumference itself, while the rest of the grain may be quite translucent. On the upper and lower sides of the surface of the grains, the needles are seen in optical section as refractive globules; in the optical plane, between the upper and lower surface, they are seen at their full length. They are tapered towards the center, resembling pyramids with a base of 2-3μ. The lamellated starchgrains in the ordinary seeds also show needles after they have been heated to this temperature. These needles extend to the first distinct non-refractive ring, and are much shorter absolutely and relatively. The needles in the ringless starch sometimes have a length of 17 to 20μ, which is about 45 per cent of the total diameter of the grain; in the field-grown seeds they are no larger than 5μ, or about 10 per cent of the diameter. Ten to twenty or more rings can be counted.

A suspension of ringless starch in water heated over a flame applied to the margin of the slide shows all graduations of swelling.