182 



THE WHEAT PLANT 



When two caryopses are present in a single spikelet the one produced 

 by the lower flower is the smaller. 



The grains of the small forms which I consider typical T. dicoccoides are 

 about 9 mm. long, 17 mm. broad, and 1-85 mm. 

 thick, the ratios length : breadth : thickness = about 

 100 : 19 : 20-5 ; 100 grains weigh from 2-2 to 2-8 gr. 

 Those of the form called " large seeded " by Cook 

 are among the longest of all wheat grains, equal- 

 ling in this respect those of 

 T. polonicum ; they measure 

 11-12 mm. long, 2-9 mm. 

 broad, and 27 mm. thick, the 

 ratios length : breadth : thick- 

 ness = about 100 : 25 : 23 ; 

 100 grains weigh from 5 to 



FIG. 1 20. Grains, front, 

 of T. dicoccoides ; front, 

 back, and side views 

 (nat. size). 



I am of the opinion that 



most of these " large-seeded " 



forms are of hybrid origin, 



and contain a trace of T. 



durum. 



The rachis of the ripe ear becomes disarticulated 

 at its joints on the slightest shake, the spikelets near 

 the apex becoming detached first, the others break- 

 ing off in orderly succession towards the base ; the 

 basal spikelets are frequently green and unripe when 

 the apical spikelets begin to fall. The short inter- 

 nodes of the rachis form beaks at the base of the 

 detached spikelets. 



Each flattened internodal beak is from 4 to 5 mm. 

 long, somewhat convex on one side and correspond- 

 ingly concave on the other, the base or free end slightly 

 curved to one side, so that the plane of the disarticu- 

 lation-scar is almost parallel to the flat side of the 

 rachis ; the scar is shaped like a narrow segment 

 of a circle. The detached spikelets after falling to 

 the ground creep into crevices and bury themselves 

 in the soil, the hairs on the rachis and the scabrid 

 awns allowing free motion in a forward direction, but effectually preventing 

 any backward movement. 



In the small-grained forms where two caryopses are present in a 

 spikelet the upper grain germinates very soon after sowing, but the lower 

 one remains dormant for a time or refuses to grow at all ; this difference 



FIG. 121. Grains from 

 the spikelets of one 

 side of an ear of T. 

 dicoccoides (nat. size). 



