298 MONOCOTYLEDONS. 



315. Wheat (Triticum vulgar e). The origin of the culti- 

 vated varieties of Wheat is very uncertain, as in the case of 

 the Broad Bean and other plants which have long been in 

 cultivation. The closest relative of Wheat among British 

 Grasses is Couch-grass, but Wheat is annual while Couch- 

 grass (like the great majority of Grasses) is perennial. 



We have already studied the germination of the Wheat 

 grain (Art. 80). In a young plant showing four or five 

 leaves note the arrangement of the leaves in two opposite 

 rows, each leaf arising from a slight thickening (" node ") on 

 the stem. Note the narrow green leaf-blade, bearing green 

 ridges, separated by white grooves, on its upper surface ; in 

 the early leaves there are about a dozen of these ridges. 

 Note that the blade has no stalk, but passes into a sheath 

 covered with soft hairs on the outside but smooth within; 

 the sheath clasps the stem, but is split down on the side 

 opposite the blade. Note the stem-clasping outgrowth, 

 or upward continuation, of the sheath at the base of the 

 blade ; this outgrowth, here long and either rounded or 

 toothed on its margin, is called the ligule. 



Trace the leaf -sheath downwards to its insertion on the 

 stem, noting the firm thickened basal part of the sheath, 

 which produces the swelling at the " node," and the softness 

 of the stem in this region. Examine plants at different 

 stages of growth. In seedlings with only four or five 

 spread-out leaves, on carefully pulling down each leaf-sheath, 

 also on slicing the whole shoot longitudinally, you will notice 

 (1) a bud in "the axil of each leaf, (2) a small swelling at the 

 tip of the stem. Later on, note that the buds have grown 

 out of the leaf -sheaths and given rise to branches, which 

 may repeat the process. By this branching or " tillering " 

 as many as fifty shoots may be produced from the basal part 

 of a single Wheat plant. The swelling at the end of the 

 stem will now show two opposite rows of projections the 

 young spikelets or "ears." 



In the ordinary kind of Wheat flowering occurs in June. 

 At the beginning of May the " nodes " are still close to- 

 gether, so that although the leaf -blades are long and well 

 developed the sheaths overlap each other. But now the 

 " internodes " of the stem begin to lengthen, spacing out the 

 leaves and carrying the shoot upwards. This elongation, 



