Also during the late 1920s and 1930s, Sears pioneered the study of fossil pollen as a cue to past vegetation and climate in the United States.

The fossil pollen closely resembles that of T. truncata, Alloxylon pinnatum as well as O. grandiflora.

The other aspect of his work built on his early agricultural and botanical training, and he became a recognised authority on fossil pollen.

Extinctions are seen both in studies of fossil pollen, and fossil leaves.

The fossil pollen closely resembles that of T. truncata, Alloxylon pinnatum and Oreocallis grandiflora.

But the fossil pollen discovered in Mexico halted this theory, and the crop is now believed to be derived solely from the prehistoric wild corn.

The fossil pollen closely resembles that of Telopea truncata, A. pinnatum and Oreocallis grandiflora.

Although the bulk of Dr. Thanikaimoni's early research dealt with pollen of modern flora, in the late 1970s turned his attention to fossil pollen as well.

Studies of fossil pollen indicate that trees recolonized these lands at an exponential rate (Bennet 1986).

But the discovery of the fossil pollen halted this theory and the corn now consumed is believed to be a direct descendant of the prehistoric wild corn.