GRAMINE^ (POACE^), GRASS FAMILY 



79 



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grass inflorescence. The spikelets are attached either 

 directly or indirectly to a main axis, the rachis (Fig. 28). 



The three common sorts of grass inflorescences are the 

 spike, j>anicle, and raceme. When the rachis is unbranched, 

 so that the spikelets are not borne on individual stalks, but 

 are attached directly (sessile) to the rachis, the result is a 

 spike. The inflorescences of wheat, 

 barley, and rye are good examples of 

 spikes. Usually, each culm bears a 

 single spike. In the raceme, each spike- 

 let is borne on a short branch of the 

 rachis, as in sheep's fescue (Fesluca 

 ovina). In the panicle, the primary 

 branches of the rachis branch one or 

 more times (Fig. 44). These branches 

 may be long and widely spreading, as 

 in oats and brome grass, or short and 

 rather appressed to the rachis, as in 

 timothy, meadow foxtail (Alopecurus) , 

 and Koeleria. 



Different types of inflorescences be- 

 sides the spike, raceme and panicle will Fig. 28.— Single spike- 



, , •.1 • J- ii_ J- 11 • let of common wheat 



be met with m some of the following (Xriticumaestivum). X2. 

 families. We shall also see that these 

 three types are not confined to the grass family, but are in 

 fact exceedingly common among seed plants of all kinds. 



Spikelet. — The spikelet is the unit of inflorescence in 

 grasses. A typical spikelet, such as that of oats (Fig. 46), 

 or wheat (Fig. 28), for example, consists of a shortened axis, 

 the rachilla, bearing a number of chaff-like, two-ranked 

 (distichous), overlapping bracts (glumes of some authors). 

 The two lowermost bracts are empty, that is, do not bear 

 flowers in their axils. Fig. 29 shows a dissected wheat 



rachij 



