Estimates of Teosinte Introgression 
Since the archaeological 'Tripsacoid cobs, like modern 
maize-teosinte derivatives, have a higher specific gravity 
than non-Tripsacoid ones and are more resistant to ero- 
sion by sulphuric acid, it is assumed for the purposes of 
this study that induration of the tissues of the cob is a 
rough measure of teosinte introgression. Estimates of 
introgression were made with an arbitrary key of five 
grades. Grade-1 designates the pure maize extreme while 
grade-5 approaches a maize-teosinte F; hybrid (Plate 
XXVIII). Although the degree of induration is the chief 
factor, single-pistillate spikelets distinguish the highest 
grade. Single-pistillate spikelets are characteristic of teo- 
sinte and are common in maize-teosinte hybrids, but ab- 
sent in typical maize. 
Other Characters Studied. Cob size has a particular in- 
terest for these studies, since previous work on archaeo- 
logical maize indicates that an enlargement of the cob has 
been an outstanding feature of maize evolution (Mangels- 
dorf and Smith, 1949; Mangelsdorf, 1954). Both length 
and diameter of cob were measured. Other characters 
chosen for analysis were kernel-row number and fasci- 
ation. Insmaller samples of the collection, the following 
internal characters were also studied: pilosity, cupule 
width, glume length and rachis diameter. Average esti- 
mates of teosinte introgression (average induration score) 
were determined for each morphological class by the use 
of key-sort cards. Correlation coefficients were then cal- 
culated and the data were plotted in curves. In the case 
of kernel-row number, however, the effects of teosinte 
introgression were studied independently for the fasciated 
and non-fasciated cobs. This distinction was made be- 
cause fasciation is known to have an effect of its own on 
row-number. 
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