2 BULLETIlSr 406, U. S. DEPARTMENT OF AGEICULTURE. 



Johnson grass, is seen to bear ise^dral sfeeds (ripened spikelets) at- 

 tached directly (sessile) at the nodes of the jointed axis (rachis) 

 of the cluster. These are indicated in figure 2 by a, which shows 

 them as occurring along only one side of the axis. Accompanying 

 these fertile or grain-bearing spikelets, which constitute the greater 

 part of the unhulled commercial seed, are several slender, sterile 

 spikelets (6), each elevated on a stem or pedicel {d) which is attached 

 with a fertile spikelet at a node of the rachis. It is to be noted that 

 the terminal fertile spikelet is accompanied by two sterile spikelets 

 with their pedicels. It is especially to be noted that in the figure 

 each node and the apex of each pedicel are marked by a distinct cross 

 line indicatmg the suture (e) at the articulation or junction of each 

 rachis segment and of each pedicel with its spikelet. 





2 



Fig. 1.— Seeds of Johnson grass (1) and Sudan grass (2). Hulled grains appear at the left of each group. 

 (Natural size, from a photograph.) 



It is the normal habit of the seed clusters of Johnson grass at 

 maturity to break apart at these sutures, thus providing for the fall 

 of the seed. Each rachis segment and accompanymg pedicel remain 

 attached to a mature spikelet or unhulled seed. Terminal spikelets 

 retain the two pedicels. The rachis segment and pedicel or the two 

 pedicels may be referred to collectively as the appendages of the seed. 



In Sudan grass the terminal seed clusters in general structure are 

 essentially the same as in Johnson grass. They differ, however, in 

 being devoid of a suture at the nodes of the rachis and apex of the 

 pedicels. In consequence, the seed fall does not imiformly result 

 from separation at the articulation, but rather from the breaking of 

 the rachis segments and pedicels at their weakest point, usually near 

 the center (fig. 3, c). Most of the unhulled seeds therefore have a 

 short stem (fig. 3, a). 



