THE INFLORESCENCE 105 



to the bottom of the ear with the longest never at the apex, while in beard- 

 less ears whatever awns are present are longest near the apex of the ear, 

 the rest rapidly diminishing in length towards the base, where they are 

 rarely more than 1-3 mm. long. 



Beardless forms are not found in T. aegilopoides, T. dicoccoides, T. 

 monococcum, T. orientale, and T. pyramidale, and are of great rarity in T 

 dicoccum, T. durum, T. turgtdum, and T.polonicum, but among the remain- 

 ing races, viz. : T. vulgare, T. compactum, T. sphaerococcum, and T. Spelta, 

 both classes are equally common, almost all the bearded varieties of these 

 wheats having a corresponding beardless representative. 



The awns are white, red, or black, those of the two former tints being 

 found only on white or red glumes respectively ; black awns are met 

 with on glumes of all colours, white, red, or black. 



Varieties with black awns are seen among all races of wheat, but are 

 most common in T. durum and T. turgtdum. They are exceptionally rare 

 in T. vulgare. I have seen but few examples of typical ears of the latter 

 race with jet-black awns ; these came from Asia Minor and Central Asia. 

 The black pigment is always most conspicuous in specimens grown in 

 bright hot climates. 



In some wheats the black colour is almost constant under a wide 

 range of climatic conditions ; in others, it is dependent on the intensity 

 of the light, heat, and moisture at the time of ripening. In cool, damp 

 seasons the black pigment in the latter forms never develops, but returns 

 in hotter years. This variation I have repeatedly observed in the progeny 

 of single ears, perhaps more especially in forms of T. durum, var. melanopus, 

 and similar results have been recorded by Metzger, Koernicke, Howard, 

 and others in different varieties. Such variation greatly reduces the 

 taxonomic value of black awns. 



The fact that external conditions of soil and climate greatly influence 

 the development of pigment in the awn complicates the problem of its 

 inheritance. 



Opposite each flowering glume, but attached to the very short floral 

 branch with its back to the rachilla is the palea, a symmetrical thin mem- 

 branous glume with two prominent lateral veins, along which runs a line 

 of stiffish hairs ; the part between the veins is concave and the two 

 semi-transparent margins curve inwards round the flower. 



STRUCTURE OF RACHIS, GLUMES, AND AWNS 



The rachis is notched, consisting of short internodal lengths, each of 

 which is convex on one side and more or less flattened on the other ; the 

 lower internodes are somewhat semicircular in transverse section, the 

 upper ones flattened and spindle-shaped in section (Fig. 80). 



