PANICLE CHABACTEE3 OF 5OEG0 19 
EXTENT AND MANNER OF SPIKELET OPENI. 
Spikelets tend to open to definite angles, which vary with the 
variety, the extent of opening being determined mainly by the 
of the caryopses as compared with the glumes, the former together 
with the lodicules as they increase in size tending to force the glumes 
open. Although some differences exist between spikelets within 
varieties as well as between those within single panicle.-, cliu 
and probably also soil conditions modifying development of the 
earyopsis somewhat, the tendency is for .-pikelets of each kind to be 
spread on the average about the same each year. The fluctuation due 
to weather conditions apparently depend- much upon the time that 
radical climatic changes occur, and as all the spikelets of a variety 
do not develop at the same time there may not. for this n, be 
absolute uniformity in the amount that spikelet- open even in il ! 
same panicle. This must be taken into consideration in estimating 
the normal amount. Both the means and range.- of angles assumed 
help to characterize certain varietal groups and also certain varie- 
ties themselves. Marked variation from the width of opening com- 
monly seen in a form may usually be considered a- denoting an im- 
purity, tlii- frequently being due to chance hybridization with an- 
other type. 
It was found better to measure the angle made by imaginary lines 
drawn from the points of insertion to the apices rather than the 
angle made by the edges of the glumes, as in some forms the edges 
are more or le.-- curved, and in those which open but slightly the 
angle made by the edges is relatively too large, as compared with 
those which open wider. The range of average angles in the varie- 
ties studied extends from about 10° or 15° to about 70° or ^0 C . In 
none of these varieties are the glumes always closed. Pech (12) and 
Collier (o) both based groups on whether the glumes were open or 
closed. 
The manner of opening also varies considerably with the different 
varieties, being due in part to the relative thickness of the first and 
second glumes at the base, in part to the relative positions of the two 
glumes, in part to their form, and in part to differences in the man- 
ner in which the earyopsis develops. In certain varieties in which 
the glumes are considerably thickened at the base both glumes yield 
about equally to the pressure exerted by the earyopsis as it incre 
in size, and even though the glumes open as much as 4" there is 
no bending back of either one of them, but because of their thick- 
ness at the base they pivot at their points of insertion. In certain 
other forms one or occasionally both glumes are either bent or folded 
back at a point somewhat above the insertion. When one jilume 
yields more than tire other the first is commonly the one mainly 
forced back, as it is inserted below the second and is outside of it. 
Usually it bends at a point just above the callus and may - irply 
doubled, so that a fold or crease is formed. In certain other varie- 
ties in which thickening is somewhat less than in those thus 
both glumes are sometimes slightly bent or cr< th yielding 
easily to the pressure exerted from within. There are. moreover. 
