130 



shortened in sandy soil, which dries quickly, and, since potassium makes the 

 corn mealy, I would much sooner believe that the action of the potassium is 

 stopped too soon and indeed because other processes, viz., those of ripening, 

 take place too early and too intensively. This will happen much more 

 quickly with strong action of light and warmth and when the water con- 

 tent is less. Sanio's' statement that in East Prussia the glassiness of 

 wheat is due to its becoming overripe on the stalk supports the theory of 

 the predominance of the ripening process at a time when starch formation 

 should be taking place. This opinion is analytically supported by R. Pott's 

 investigations- who found on an average a higher percentage of ash in 

 glassy varieties of wheat than in mealy kernels. The kernels, in the too 

 rapid ripening, had not completely consumed the mineral substances in 

 forming organic substances. Compare here the high percentage of nitrogen 

 in the grains of oats plants, which suffered from a scarcity of water or 

 from its excess (see chapter, "Excess of Water"). 



Petri and Johannsen' have made investigations which throw much 

 light on the nature of glassy kernels. The former, as early as 1870, stated 

 that glassy kernels, when softened by water, become mealy and the latter 

 substantiated this observation. Two hundred kilos of barley were moistened 

 with half that amount of water, until they had taken up 15 per cent. They 

 were then dried immediately, spread and turned until the original weight 

 was again obtained. The percentage of mealy kernels now was 50 per cent., 

 while in the original material it amounted to only 19 per cent. In cultural 

 experiments it was found that, in early seeding, a mealier barley, poorer in 

 nitrogen, had been formed, while in later sowing the harvested product was 

 richer in nitrogen. This discovery indicates that in this glassiness of the 

 kernels there is only a mechanical difference, which develops if ripening is 

 very much hastened by a scarcity of water with an excess of light and 

 \varmth. A gradual ripening process gives a longer time for developing an 

 increased starch content with the retention of a larger water content in the 

 substance which is later partially replaced by air. This refers especially to 

 the protoplasm in the endosperm cells. The starch grains lie embedded in 

 this. With quick ripening, the cytoplasm sticks close to the starch grains, 

 making the kernels appear glassy. With slower ripening and greater water 

 content the cell is more loosely constructed, while between the starch grains 

 more cell sap and later more air are present, and then, because of the larger 

 intercellular air spaces, the grain is opaque and mealy. As the protoplasm 

 predominates, the tendency is toward glassiness, and on this account, even 

 normally, the outer layers of the seed, as, for example, in maize, are glassy, 

 the inner ones mealy. These conditions explain .Schindler's observations* 

 that, in wheat grains, mealy and glassy portions can alternate. 



1 Botanisches Centralbl., 1880, p. 310. 



- Jahresbericht f. Agriculturchemie 1870-72, II, p. 5. 



3 Johannsen, Bemerkungen tiber mehlige undglasige Gerste (Ugeskrift for 

 Landsmaend), 1887, cit. Biederm, Centralbl., 1888, p. 551. 



4 Schindler, Lehre vom Pflanzenbau auf physiologischer Grundlage. Wien 1896. 



