THE GRAIN 19 



I have usually found that the small spikelets near the base and apex bear 

 a greater proportion of mealy grains than the larger spikelets from the 

 middle of the ear, and the lower heavy grains of each spikelet are usually 

 more flinty than the smaller upper ones. 



The flinty grains of any pedigree line wheats are, on an average, not 

 only larger and heavier than those of the same sample with mealy endo- 

 sperm, but have a higher specific gravity than the mealy grains. 



Investigations of two examples gave the following results : 



The flinty grains in these wheats are usually 7-10 per cent larger, 

 10-12 per cent heavier, and have a specific gravity 3-4 per cent higher 

 than that of mealy grains. 



The white opaque appearance of the endosperm of mealy grains is due 

 to the presence of minute fissures, which develop between and within the 

 cells during the dessication which occurs at the time of ripening of the grain. 



On examination of carefully prepared transverse sections x from grains 

 showing different degrees of mealiness, it is seen that interstices have 

 formed along the line of union of adjacent cells and around the starch 

 grains within the latter, and the contents of some of the cells have shrunk 

 more or less away from the surrounding cell wall ; these changes appear 

 first near the furrow, and spread radially outwards across the endosperm 

 towards the aleuron layer on the dorsal side, especially in the basal half 

 of the grain near the embryo. 



Minute irregular cavities are seen also in the aleuron cells. 



From investigations on mealy grains of barley, Brown and Escombe 

 concluded that the interstices are vacuous or only partially filled with air. 



Such minute spaces are absent from flinty endosperm in which all 

 the cells of the tissue are completely filled with starch grains imbedded in 

 a protoplasmic matrix, the whole forming a dense coherent mass. 



The production of flinty or mealy grains is a hereditary character of 



1 The endosperm of uninjured flinty grains appears to be under a stress which tends 

 to rupture the cells and cell contents, and thin sections cut from flinty grains immedi- 

 ately become opaque and " mealy." To obtain sections sufficiently thin to be examined 

 with a high power, without disturbing the original physical condition of the endosperm, 

 thick dry sections may be ground down on a " carborundum " stone with the finger-tip. 

 Examine the sections in oil or Canada balsam. 



