O. N. Purvis 353 



greater rigidity was found in the material whiclr had received potash, 

 but this was not the case in Plots 7 and 8. 



There was little difference between the wall thickness (shown in 

 Fig. 21) in material from Plots 9 and 10; on May 31st and June 26th the 

 thickness was greater without potassium salts, but on the two inter- 

 mediate dates it was greater where they had been applied. 



The lumen was considerably greater where potash was present on 

 May 31st and June 26th, but on the two intermediate dates the plants 

 which had been treated with potash had xylem vessels with smaller 

 lumina (Fig. 22). 



As the wall thickness was practically unaltered throughout, the ratio 

 of lumen to wall, and therefore the mechanical strength of the cells 

 (assuming as in other cases the similarity of wall material), was deter- 

 mined by the width of the lumina (Fig. 23). 



In the case where nitrogen fertilisers were not applied the effect of 

 potash on the xylem vessels is indefinite. 



Summary and Conclusion. 



Stems of Dactylis glonierala were collected from grass-plots which 

 had received different manurial treatment as regards potash. 



The yield of hay from these plots was in close agreement with the 

 average which shows that the season during which the work was done 

 was not abnormal. 



The thickness of the wall, the diameter of the lumina and the ratio 

 of the lumen to the wall were measirred both in sclerenchyma and meta- 

 xylem elements. 



It was found that in the early stages the sclerenchyma walls were 

 thinner where potash had been supplied, but that this effect was lost 

 as the season progressed. 



The lumina were larger in plants which had received potash, when 

 nitrogenous fertilisers had not been added, but in the presence of 

 ammonium salts, this effect was reversed. 



In the xylem the thickness of the walls was unaltered whether 

 potassic fertiliser were added or not. When no nitrogenous manures 

 were added the diameter of the lumen was decreased in the presence of 

 potash, but when ammonium salts had been apphed, the diameter was 

 increased by the application of potassic fertilisers. 



The addition of potassium salts produced an increased ratio of lumen 

 to wall but this effect gradually passed off. Presumably, therefore, 



