are the only New World grasses so far investigated which 
‘cannot be distinguished from maize by a simple measure- 
ment i.e. > 45 for the long axis, and >5.7p for the pore- 
axis ratio. 
We believe that 777psacum conforms to Rowley’s first 
type in possessing three levels of phase retardation ; maize 
to the second type. ‘Teosinte in some varieties appears to 
have a faintly incised reticulum and hence is intermediate 
in this optical characteristic. 
In this study, pollen grains were prepared from a num- 
ber of races of maize, teosinte, and two genotypes of 
Tripsacum. A list of these is found in ‘Table IT. In all 
‘ases, several anthers, selected from more than one tas- 
sel and more than one plant if specimens were available, 
were utilized in order to avoid the influence of an unusual 
genetic constitution in a single anther or single plant. 
All available varieties of teosinte in the Botanical Mu- 
seum of Harvard University were examined. An attempt 
was made to choose examples from a number of groups 
of maize from diverse geographic sources. A > muaize- 
Tripsacum hybrid (WM'T maize X T. dactyloides) and 
two varieties of maize bearing one or more known teo- 
sinte chromosomes were studied. In addition, several 
grains trom the fossil record were examined. 
All preparations were made by the use of standard 
acetolysis treatment, followed by bleaching, and the 
grains were mounted in glycerine jelly. Photographs 
were taken with a Zeiss Opton W > microscope, employ- 
ing phase objectives on both 85 mm. and 4X5” high 
contrast film (Microfile and Contrast Process Pan). The 
2” 2" photographs in Plates ILI-VII were made on 
4X5" negatives. 
As these photographs indicate, 7'ipsacum can be dis- 
tinguished from maize and teosinte by use of phase op- 
tics. In Toipsacum, the spinules are distributed irregu- 
(40 | 
