GRAMINEAE 



The florets are borne singly on an axis, the rachilla, (Fig. E) which disarticulates 

 usually below each floret, the rachilla- joint remaining attached at the back of the palea. 

 (Fig. C). In some 1-flowered spikelets the rachilla is prolonged behind the palea as a 

 slender, often hairy, bristle. 



Below the florets are 2 bracts (the glumes), the first wanting in a few genera 

 (Fig. F). The glumes, rachilla, and florets together form the spikelet, which is a 

 flowering branch (Fig. G) reduced to the essential organs. This simple arrangement 

 is modified in various ways, but everything in any spikelet can be identified by its 

 position as one of these organs. Glumes and lemmas are often hairy or variously 

 nerved, the nerves sometimes extending into awns. 



Before studying the spikelets one must observe the relatively few specializations 

 of the vegetative parts. As in other plants, stems or parts of stems may be under- 

 ground (rhizomes or rootstocks), borne at the base of the main culm under the earth. 

 They are jointed like the culms and bear scales which correspond to leaves; shoots 

 are produced in the axils of the scales as branches are borne in the axils of leaves. 

 Sod-forming grasses have this kind of underground stem (Fig. H). In some grasses 

 the shoots from the base extend over the surface of the ground instead of beneath 

 it. Such shoots are stolons. Both rhizomes and stolons produce roots from the nodes. 

 Bermuda grass produces either rhizomes or stolons and sometimes both from the same 

 plant. 



Grasses may be annuals, germinating, seeding and dying in a single season, like 

 the weedy bromes and wild oats, or perennials like orchard grass, Bermuda grass, 

 and the long-lived bamboos. 



It is chiefly by the modifications of the spikelets and their arrangement in the 

 inflorescence that grasses are classified into genera and tribes. Theoretically the 

 spikelet is a reduced leafy branch. In the generalized spikelet shown in Fig. E the 

 likeness to a jointed culm with 2-ranked leaves (Fig. G) is readily seen, the glumes 

 and lemmas corresponding to sheaths, their blades not developed. The palea, with 

 two nerves and with its back to the axis, corresponds to a minute bract (the prophyllum) 

 borne at the base of a branch in the axil of a sheath. The prophyllum is always 2- 

 nerved, with its back (that is, the space between the nerves) against the main axis 

 and its margins clasping the young branch. The flower, also, is theoretically an 

 ultimate branchlet. In the flower-bearing lemmas, therefore, the palea is developed, 

 while in the glumes, bearing no flowers, there are no paleae. Glumes and lemmas 

 are, morphologically, reduced leaves, the lower pair, not flower-bearing, being termed 

 glumes, the flower-bearing ones being termed lemmas. (See Fig. E.) 



The jointed axis of the spikelet (the rachilla) corresponds to the jointed culm and, 

 like it, usually breaks at the nodes, the internode (the part of the rachilla between 

 two nodes) remaining attached to the floret at its base (Fig. G), just as in a broken 

 grass stem the internode of the culm remains with the sheath that surrounds it; that 

 is, the break normally comes just under the node. Rachis (which means the spine, 

 or backbone) and axis (the imaginary central line of any body) are often used inter- 

 changeably as botanical terms. In most recent works on grasses and in these descrip- 

 tions, axis is used for the main axis of a compound inflorescence, rachis for the axis 

 or support of the spikelets. In Fig. I 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 (with- 

 out a pedicel) in leafless panicles, racemes, or spikes. These different types of 



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