1.* A further complication of measurement results from 
size changes induced by various sedimentary environ- 
ments and various preparatory techniques (Anderson, 
1960). 
The exine itself, except for the pore, consists of an 
endexine, an ektexine tegillum supported by columellae, 
and simple spinules projecting from this tegillum and 
corresponding in arrangement to the columellae. With 
ordinary light microscopy, this exine appears smooth, 
while, with phase-contrast, the spinules appear as a pat- 
tern of dark dots. Using phase-contrast microscopy, 
Grohne (1957) investigated the pollen of ‘*wild™” and 
cereal type grasses in Europe and suggested that dis- 
crimination between the two was possible on the basis 
of certain phase changes in this exine pattern (see also 
Erdtman and Praglowski, 1959). 
An explanation of these phase changes was offered by 
Rowley (1960). He found that grasses of the ‘‘wild 
type’’ have three levels of phase retardation. The lowest 
is that resulting from depressions between the spinules. 
These depressions form an incised reticulum that may 
have one to several spinule per lacuna. This reticulum 
under phase appears as a dark network. The two other 
regions of phase retardation are the level ektexine sur- 
face (non-incised interspine regions) and the spinules 
themselves. Grasses of the cultivated type have only 
two areas of phase retardation, the level ektexine, and 
that of the surmounting spinules. Rowley’s investiga- 
tions were aided by the use of an electron microscope. 
The present paper presents results of observations of 
the exine, using phase-contrast light, in the New World 
plants maize, teosinte, and T'ripsacum. The latter two 
* The data presented in this figure were drawn from the measure- 
ments of James Langham and Professor Donald Whitehead. Used by 
permission of Dr. Whitehead. 
[ 38 | 
