withstand \en- well a continued contact with running or standing water, 

 which is free from organic substances, as can be seen in the di liferent water 

 cultures. Here, however, all living or dead vegetable particles in the culture 

 vessels are avoided, for the decomposing organic substances take up all the 

 oxygen which is present in a small supply. The roots of the growing plant 

 must be killed because of a scarcity of oxygen and excess of carbon dioxid. 

 Also, under ordinar}' conditions, seeds can survive contact with water, 

 lasting for weeks, if the temperature is low. Thus Feige^ states that wheat 

 which had stood for 5 weeks under cold water at 5°C. still lived. On the 

 other hand, wheat kept 8 weeks under water, the temperature of which in- 

 creased to y^C had disappeared without leaving a trace. Corn, which had 

 previously been healthy, withstood water at 3°C. for 4 or 5 weeks, but was 

 injured somewhat more than the wheat mentioned above. In the same way, 

 alfalfa and clover withstood standing in water better than did com. 



According to Kiihn, rye suffers especially from souring, while under 

 the same conditions brome grass and others develop very luxuriantly. To 

 this circumstance is due the erroneous belief, which even now occasionally 

 appears, that rye can change into brome grass. According to our view, 

 "Arrabbiaticcio" of wheat in Marengo and on the Roman Campagna be- 

 longs under this head. Peglion- explains the disease as a general deteriora- 

 tion of the plants due to being overrun by the luxuriant growth of weeds, 

 which thrive better than the wheat on unsuitable soil. In Southern Italy the 

 disease is called "calda fredda" and "secca molla." 



The souring of the winter oil seeds, especially rape, is the most serious 

 of all. From standing continually in water the roots decay from the tips 

 backward so that in spring only the crown of the root and the leaf rosette 

 remain. These appear to be healthy as long as the moist spring weather 

 prevents their drying out, yet, as the season becomes dry, the plants turn 

 brown very soon and may be drawn from the soil by one leaf. 



An investigation by E. Freiberg and A. Mayer'' serves to explain the 

 fact that under continued wet conditions the character of the vegetation 

 changes, so that phenomena appear like the above mentioned predominance 

 of brome grass when rye had been sown. This experiment proved that the 

 roots of marsh plants need much less oxygen than those of cultivated plants. 

 This proves, as might have been supposed from the very beginning, that the 

 individual plant species make different demands on the oxygen of the soil 

 and, accordingly, must adjust their habitat to existing conditions. From the 

 result of the experiments, however, another conclusion may be drawn 

 which may serve in general when judging the demands made by different 

 plants on soil; viz., the amount of air needed by their root systems. It 

 is found that the more oxygen the plant needs for respiration, the greater is 

 its nitrogen content. Marsh plants show a strikingly low nitrogen content and 



1 From Oesterr. landw. Wochenbl. cit. in. Biedermann's Cemtralbl. 1877, p. 76. 



- Peglion, v., Sull' arrabbiaticcio e calda freddo. Annuar. d. R. Stazione di 

 Patol. veget. Roma. Vol. I, 1901, p. 37. 



'•'' Freiberg-, K, und Mayer, A., Ueber die Atmungsgrofse bei Sumpf- und Wasser- 

 pflanzen. Landwirtsch. Versuchsstationen 1879, p. 463. 



