Piate XI. Transitions from teosinte to maize il- 
lustrated by the pistillate spikes of F2 segregates 
of a maize-teosinte hybrid. A. Most teosinte-like 
spike with single spikelets alternating in two ranks. 
B, C. Transition from independent to yoked rachis 
segments. D. Approximately like A, except that 
spikelets are paired. E. Yoked rachis segments 
combined with paired spikelets to produce a dis- 
tichous, four-rowed spike, bearing four spikelets at 
each joint of the rachis. F. Portion of spike and 
single rachis joint of an eight-rowed spike derived 
from a four-rowed spike by “‘twisting’’ of the axis. 
G. Most maize-like spike. It differs from F pri- 
marily in degree of compaction, 
Pirate XII. The arrangement of sessile and pedi- 
cellate spikelets around the circumference of va- 
rious spikes. A. Teosinte spike. B. Teosinte spike 
with yoking of rachis segments. C. Theoretical 
arrangement resulting from yoking combined with 
twisting of the axis. D. Actual arrangement of 
spikelets on a portion of the central spike of the 
tassel of an inbred strain of Guarany maize. Note 
that arrangement is random or nearly so. E. Ac- 
tual arrangement on a portion of the central spike 
of North American inbred K155. Note that ar- 
rangement is strongly systematic. 
[75 | 
