LESSON XII 



HIGHLY SPECIALIZED UNISEXUAL 

 SPIKELETS 



Examine Fig. 80, 

 gama-grass {Tripsacum 

 dactyloides) . This grass 

 is monoecious (see p. 23). 

 The pistillate spikelets 

 are borne on the lower 

 part of the one to three 

 stout digitate racemes 

 and the staminate spike- 

 lets on the upper part of 

 the same racemes (Fig. 

 80, D). The part of the 

 rachis bearing the stami- 

 nate spikelets is rela- 

 tively slender and falls 

 off after flowering time; 

 the part bearing the pis- 

 tillate spikelets is greatly- 

 thickened and disarticu- 

 lates with the spikelets 

 permanently embedded 

 in the joints. Fig. 80, A, 

 shows two joints with 

 spikelets embedded; B, a 



Fig. 80. A, two joints of pistillate 

 part of raceme of Tripsacum dac- 

 tyloides; B, spikelet removed from 

 tjie joint; C, rachis joint from 

 which spikelet has been removed; 

 D, inflorescence; E, diagram of 

 rachis of pistillate part; F, pair 

 of staminate spikelets. 



89 



