28 BULLETIN 1386, IT. S. DEPARTMENT OF AGRICULTURE 
a short time. The feasibility of using variations in these features as 
varietal characters will depend upon whether or not other more 
plainly marked and easily seen characters are available. 
SEX 
• Stamens are found in some forms, and though they are small and 
are usually at the base of the spikelet, in certain varieties they show 
further development. Short filaments are also sometimes found in 
connection with them. 
VARIETAL GROUPS 
In presenting the grouping of varieties which follows, no claim is 
made for its originality in every detail. Considered from the view- 
point of resemblances between the varieties such a classification seems 
a natural one. and for this reason it has been adopted. 
It is the aim to show general similarities and some less important 
points of likeness as well in a number of varieties considered as a 
series extending from the much-spreading to the very compact form. 
It is also the purpose to show how some of the characters described 
in preceding pages are concerned in the progressive differentiation of 
the forms. Such an arrangement of these varieties might not be the 
most adaptable one in a key for identification on account of the close 
resemblance of some of them. 
The major groups seem naturally to be subdivided with respect to 
certain characters of the spikelet. The order of rank in which the 
characters by which the varieties are separated into classes and 
subclasses are considered is as follows: (1) Relative compactness of 
the panicle, (2) comparative exsertion of the caryopsis, (3) relative 
degree of thickening in the glumes, (4) form of spikelets, and (5) 
color of spikelets or caryopses or special features of the panicle or 
spikelets. The varieties may be divided into three main groups: (1) 
Effuse, (2) contracted, and (3) compact. In each group the forms 
nuiy differ in three main characters, relative length of glumes, thick- 
ness of the glumes, and the shape of the spikelets. In the synopsis 
which follows, in order better to correlate these characters, the cor- 
responding subdivisions are indicated by A, AA, AAA; B, BB, 
BBB ; C, CC, CCC. This lettering is followed even though all the 
groups are not represented by known varieties, in which case the cor- 
responding lettered divisions are omitted. 
It is to be noted from the synopsis that in general as the type of 
panicle becomes more contracted the glumes become relatively 
shorter. That elliptic spikelets are also relatively less abundant in 
the more contracted forms also seems apparent, and this may or may 
not be substantiated with further studies of the sorghums. Certain 
other points of similarity between varieties within groups became 
evident in the course of the study. Some of these have been indicated 
in preceding paragraphs. These and other points of resemblance are 
brought out in the group descriptions and in the descriptions of the 
several varieties. 
The group taken as the initial one is the effuse, and the variety 
chosen to represent it is known in our records as Minnesota Amber. 
There are a number of somewhat similar kinds more or less com- 
monly known by this name, but this one seems to conform best to 
