352 Tlie Effect of Potassium Salts on Dactylis glomerata 



were almost equal. The efiect of potassium salts on the walls was very 

 similar to that observed in the absence of nitrogen fertilisers; with these 

 salts the walls are considerably thinner, in the early stages, but this 

 difference is diminished as the season goes on. 



A. Sderenchyma. 

 Plot 10. Ammonium salts + minerals without potash. 



During the first period the mean lumina were equal but after May 

 31st the means were slightly higher in the material without potash. 

 During the first week in June there was a sudden increase in lumen in 

 Plot 10 material similar to that observed in Plot 7 (full minerals), and 

 a similar increase occurred between June 15th and June 26th (Fig. 19). 



B. Xylem. 

 Plot 10. Xylem. Ammonium sulphate + minerals without potash. 



Date May 31st June 8th June 15th June 26th 



Walls 2-21/i 202^ 204^ 2-42^ 



Lumina 29-4^ 34-7m 30-9/i 31-7/i 



Ratio 13-60 17-83 15-27 13-30 



Plot 9. Xylem. Ammonium sulphate + full minerals. 

 Walls 1-87M 2-27m 2-16m 2-08^ 



Lumina 36-3^ 32-6^ 28-35,n 35-7/i 



Ratio 20-49 14-83 13-62 17-49 



On May 16th the ratio of lumen to wall in Plot 9 material was much 

 higher than that in material from Plot 10 (Fig. 20), a result which is 

 consistent with that obtained from Plots 7 and 8. On May 31st, and 

 on subsequent dates, the readings for the two plots were almost equal; 

 only on June 26th was the difference significant, and there the plants 

 which had received potassium salts had the lower ratio. Again, on the 

 view already expressed, the result obtained would imply that there is 

 greater mechanical strength in the cells of the sderenchyma where no 

 potassium salts had been applied, but that the difference becomes less 

 as the season advances. In the presence of nitrogen, by June 26th, the 



