SESSILE SPIKELETS IN TWO-SIDED SPIKES 37 



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is always above the first glume. 

 When no glume is found below the 

 first floret, it is obvious that it is the 

 first glume which is suppressed. 



In Fig. 28 (Lepturus cylindri- 

 cus) we have a greatly thickened, 

 strongly nerved rachis with spike- 

 lets placed as in Fig. 27 but reduced 

 to the second glume and a single 

 floret. This little spikelet is sunken 

 in the hollow of the rachis joint, 

 the second glume fitting snugly 

 over the hollow, the whole forming 

 a long, slender, wiry cylinder. At 

 maturity the rachis disarticulates 

 wdth the spikelets firmly embedded 

 in the joints. (See diagram of 

 rachis, Fig. 28, B, and, above, a 

 joint with spikelet removed, show- 

 ing the hollow, and a second with 

 the spikelet in position.) The plant 

 bearing these spikes grows along 

 mud flats near the sea. The rachis 

 joints are cylindrical and readily 

 roll down the slope to the water. 

 Being corky, they are carried by 

 the lightest ripples and are thus 

 spread over wide areas. The grain 

 germinates within its little cell, and the young roots 

 and leaves push aside the water-soaked glume. 



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Fig. 28. A, part of 

 spike of Lepturus 

 cylindricus; B, dia- 

 gram of rachis, 

 spikelets removed; 

 above, diagram of 

 single joint. 



