278 



Change ix Production Due to Lack of i^Joisture. 



The difference in the harvest yield, resulting from a lack of moisture, has 

 also been considered in previous divisions, so that here we need cite supple- 

 mentarily only a few other cases. Hellriegel's^ experiments are most de- 

 cisive. Two tests of clover were taken from a field, in which, in places, the 

 plants had begun to wilt. There was found : — 



In wilted plants Leaves 71.0 per cent, water, petioles 78.4 per cent. 



Leaves 7 1. 1 " " water, petioles 80.8 " 

 In turgid leaves among 



the wilted ones Leaves 82.5 " " water, petioles 90.0 " " 



The wilted leaves contained in the leaf-blades ca. 29 per cent, of dry 

 substances; in the petioles, 19 to 21 per cent.; while the turgid leaves con- 

 tained in their leaf-blades 17.5 per cent, and in the petioles 10 per cent., — i. e., 

 only about half that of the wilted plants. 



An example of the influence of drought on grain is given by Prianisch- 

 nikow's" investigations, according to which the nitrogen content increases in 

 corn, if the moisture decreases. Stahl-Schroeder's^ studies give a more 

 detailed representation of the influence exerted by the taking up of nutritive 

 substances and their assimilation in dry years. After mentioning the well 

 known fact, that phosphoric acid hastens ripening, while nitrogen and potas- 

 sium delay it, he notes the importance of the months before blossoming for 

 the taking up of the nutritive substances. If the soil moisture is deficient at 

 this time, the organic substances will be in smaller quantity. But the nitric 

 acid, which penetrates easily through the cell walls, will find its way into the 

 plants and in its turn again incite the taking up of phosphoric acid, in order 

 to effect the formation of the proteins. In this way, in dry years, scanty 

 harvests are produced with a high nitrogen and phosphoric content. The 

 nitrogen increase becomes the more evident, since, with drought, the grain 

 stores up the starch with much greater difficulty. The reverse may be de- 

 termined in the Norwegian com tests, the high absolute weight of which is 

 caused by an abundant starch deposit. This is explained by the growth of 

 the grain with abundant moisture under the influence of the long days. 



In Hellriegel's experiments with barley, in pots filled with sand, we 

 find, expressed in exact figures, the lowering of production, as the amount of 

 moisture at the disposal of the plant is reduced. 



Soil moisture in percentages Dry Substance 



of saturation capacity. in wStraw and Chaff in Grain 



80 — 60 7394 mg. 4896 mg. 1 averages 



60—40 5988 " 4133 " \ for 



40 — 20 4842 " 7942 " J 3 Plants 



1 Loc. cit. p. 544. 



2 Prienischnikow, Ueber den Einfluss der Bodenfeuchtigkeit auf die Entwicklung 

 dei' Pflanzen. Journ. f. experim. Landw. 1900. Vol. I, p. 19. 



3 Stahl-Schroeder, Kann die Pflanzenanalyse uns Aufschlufs iiber den Gehalt 

 an assimilierenden Nahrstoffen geben? Journ. f. Landw. 1904. cit. Biedermann's 

 Centralbl. f. Agr. Chem. 1905. Part 2. 



