HOW TO KNOW THE GRASSES 



stigmas. All grasses are wind pollinated except the few which are 

 self pollinated within closed florets (cleistogamous). The lemma has a 

 midrib and a number of smaller "veins" or "nerves" running roughly- 

 parallel to it, but converging toward the tip. The midrib of the lemma 

 may be prolonged into a beard or bristle, called an awn. Rarely the 

 lateral nerves also protrude. If the lemma is prominently folded along 

 the midrib, it is said to have a keel. The hardened lower end of the 

 lemma is called a callus. The palea always has two veins near the 

 sides, but lacks a midrib. In some grasses the palea is small or lack- 

 ing. Usually the spikelet has a stalk or pedicel, or this may be absent, 

 as in wheat and rye, and then the spikelet is said to be sessile. Usually 

 spikelets break up at maturity into individual florets, each of which 

 will then bear a segment of the rachilla. Some spikelets, like those of 

 switch grass and foxtail grass, do not break up, but are shed from the 

 plant whole. 



Often it is necessary to determine 

 at what points the spikelets break or 

 disarticulate. When the spikelets are 

 mature and dry, they will disarticu- 

 late naturally, but if one has a rather 

 immature plant, it may be necessary 

 to tease the spikelets apart with 

 needles and tweezers or with the 

 finger nail in order to tell where the 

 disarticulation will occur. There are 

 two general types of disarticulation: 

 below the glumes (Fig. 7, a), and above the glumes (Fig. 7, b). Spike- 

 lets which disarticulate below the glumes leave nothing on the plant 

 except the stubs of the pedicels. Those which disarticulate above the 

 glumes leave them on the plant. Spikelets of this type usually dis- 

 articulate between the florets as well. 



Another feature of the spikelet which we may need to know is its 

 shape in cross section. Spikelets may be round in cross section (Fig. 

 8, a), or flattened from the sides of the glumes and lemmas (laterally 



Figure 7 



b V 



Figure 8 



6 



