18 



FIRST BOOK OF GRASSES 



the sheath 

 normally comes just under 

 (which means the spine, or 

 (the imaginary central line 



that surrounds it; that is, the break 

 the node. Rachis 

 backbone) and axis 

 of any body) are 

 often used inter- 

 changeably as bo- 

 tanical terms. In 

 most recent works 

 on grasses and in 

 these lessons, axis 

 is used for the 

 main axis of a com- 

 pound inflores- 

 cence, rachis for 

 the axis or sup- 

 port of the spike- 

 lets. In Fig. 10 

 are shown the axis 

 of a panicle (A) 

 and the rachis of 

 a raceme (B) ; the 

 rachis of the spike 

 (C) is concealed by the overlapping spikelets. 



Spikelets are borne pediceled (that is, on a pedicel 

 or foot stalk) or sessile (without a pedicel) in leafless 

 panicles, racemes, or spikes (Fig. 10). These different 

 types of inflorescence insensibly grade into each 

 other. The axis and branches of a panicle and the 

 rachis of a raceme or spike may be as elaborately 

 modified and specialized as may be the parts of a 



Fio. 10. Forms of inflorescence: A, panicle; 

 B, raceme; C, spike. 



