350 The Effect of Potassium Salts on Dactylis glomerata 



decreases the thickness of walls and increases the lumen (9). Before 

 the effect of potash in the presence of nitrogenous manures can be 

 properly investigated, it is necessary to observe the effect of these 

 manures themselves. For this purpose material from Plot 7, receiving 

 full minerals, was compared with that from Plot 9, where full minerals 

 and ammonium sulphate had been applied. This addition produces an 

 alteration in two factors governing growth; firstly the amount of nitrogen 

 is greater, and secondly the acidity of the soil is increased by the libera- 

 tion of SO4 ions. Possibly this acidity may account for the small amount 

 of Dactylis to be found on Plots 9 and 10. 



Comparison of Plots 7 and 9. 



A. Sclerenchyma. 



Plot 9. Sclerenchyma. Full minerals + ammonium sulphate. 



The walls of plants grown on Plot 9 (Fig. 12) which received nitro- 

 genous manure were, on the whole, thinner than those from Plot 7, but 

 this difference was not maintained throughout the period of investiga- 

 tion. On two occasions, after the unexpected falls in the mean for Plot 7, 

 the thickness was greater where nitrogen was applied. Plot 9 material 

 gave a steady increase from beginning to end. 



Contrary to expectation, the addition of nitrogen fertiliser did not 

 increase the lumen, indeed, if anything it decreased it. From Fig. 13 it 

 is clear that the mean for Plot 9 material, which has received ammonium 

 salts, was slightly below that for Plot 7 on every date but May 31st, but 

 the difference throughout was hardly significant and the course of the 

 two curves was similar. 



At first as can be seen from Fig. ]•! the ratio of lumen to wall was 

 higher in Plot 9 material than in that from Plot 7, but as the season 

 progressed the difference became less marked until finally the means 

 were practically equal. 



The efiect of nitrogen was not well marked. The cell-walls were 

 thinner in the early stages only, but the diameter of the lumen was not 



