12 BULLETIN 1386, 'U. S. DEPARTMENT OF AGRICULTURE 
ing types of panicle than in the more compact types. Under moist 
conditions these pulvini become turgid, causing the branches to ex- 
pand, and the panicle thus tends to open; but in periods of dryness 
the pulvini tend to lose some of their turgidity and to contract, the 
branches then closing up to a greater or less extent. Continued 
humidity, moreover, nas a further effect on the panicle, especially 
after it has reached approximate maturity, the branches then all be- 
coming permanently more or less bowed and the pulvini losing much 
of their power of expansion and contraction after the panicle reaches 
maturity. As a result of these conditions all the branches tend 
permanently to stand out somewhat from the axis. For these reasons 
no sharp lines of distinction can be drawn between the spreading and 
the compact or between the spread inn. semicompact, and compact 
types of panicle. 
In a general way certain distinct forms of panicle are also recog- 
nizable, these being mainly due to variations in the length of the 
axis and in the length of the branches originating at different points 
in this length. By considering form and degree of compactness to- 
gether certain rather more definite types are recognizable, as follows : 
(1) The spreading conical, (2) the semicompact conical, (3) the semi- 
compact cylindric, (4) the compact oval, and (5) the compact cylin- 
dric. When, however, it is attempted to use these types of panicle as 
varietal characters, difficulties are sometimes encountered, as the 
variations within varieties, fluctuations, and changes which take place 
during the period of anthesis and subsequently often alter the form ; 
but the relative length of the axis and the branches and the length of 
branches originating at different points may both be taken as in 
part indicative of the form and so may help to establish the type, as 
these characters do not change materially after the spikelets have all 
reached complete anthesis. In the typical conical spreading form 
the primary branches or rays originating at the base of the panicle 
are the longest, being usually two-thirds or three-fourths as long as 
the panicle itself, and those originating at points higher up being 
successively shorter. In the cylindric form, which is at the other 
extreme, the primary branches are more nearly equal in length, none 
of them usually exceeding half the length of the panicle. In certain 
varieties which have a cylindric form of panicle, however, the lower 
primary branches in some of the panicles are considerably longer 
than those originating above them and have a tendency to be ap- 
pressed to the axis; and these panicles on this account, although they 
are cylindric, do not differ from those of certain varieties in an inter- 
mediate class in relative length of the branches originating succes- 
sively on the axis. 
The length of the internodes of the axis and of the branches and 
the comparative rigidity of the branches both indicate to a certain 
extent the type of panicle. Rigidity is, however, somewhat depend- 
ent upon length, branches showing the greatest rigidity not being 
relatively thicker, as compared with others, so much as they are 
relatively shorter, rigidity also being much subject to fluctuation and 
somewhat dependent on state of maturity. It is sometimes not 
possible, therefore, to note differences in this characteristic between 
the panicle branches of certain varieties which are properly classed 
in separate groups. In the same way the length of the internodes 
