Discussion
It is interesting to note that many of the plants identified from their megascopic remains by Walton C. Galinat are likewise represented in the pollen flora (e.g., Allium, Quercus, Juniperus and chenopods). As Galinat has also identified several fragments of Zea Mays, it was hoped that pollen of Zea might be found in some of the oldest levels. Unfortunately, none of the fossil grass pollen can be definitely identified as that of Zea. It seems obvious that the three largest grass grains (over 70ₘ) are too large to be Tripsacum, but whether they represent teosinte or Zea can not be established. The pore of two of these was obscured by detritus, and that of the third was greatly distorted. Thus no ratio could be established.
The remainder of the grass grains seem to fall within the limits of the genus Tripsacum (size extremes 33.6ₘ to 64ₘ, and ratio extremes 1:3.0 to 1:4.8), although the pore-axis ratio of some appears to be too large. However, the possibility must be left open that these smaller grains might not be Tripsacum. As yet there is very little pollen size data available for the grasses of North America. Geisler (1945) has measured pollen from 32 species and of these, Zizania aquatica has the largest grains (range 38ₘ-50ₘ). It is important to note that she did not employ acetolysis, so that this range is on the small side. In Europe, Firbes (1936) has presented pollen size data for 103 species of grasses, and of those he studied, Avena, Secale, Triticum, Hordeum, and Elymus possess pollen as large as that of Tripsacum. Hence it would appear to be necessary to study intensively the pollen of most of our native grasses in order to establish size and other morphological criteria for identifying the smaller LoDaisKa grass pollen.
As the preservation is distinctly better in the lower levels of the deposit, a careful and detailed pollen analytical investigation, with recourse to adequate reference material might be profitable.
Acknowledgments
The present investigation was carried out in the Laboratories of the Geological Survey of Denmark while the author was sponsored by a Fulbright Fellowship. The author is particularly indebted to Svend Th. Andersen for his suggestions and helpful criticisms of the manuscript.
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