33 



VI. O. N. Purvis. " The Effect of Potassium Salts on the 

 Anatomy of Dactylis Glomerata.'' Journal of Agri- 

 cultural Science, 1919. Vol. IX. pp. 338-365. 



Stems of Dactylis glomerata were collected from grass plots 

 w hich had received different manurial treatment as regards potash. 



The yield of hay from these i)lots during the period of the in- 

 \ t^^tigation was in close agreement with the average, showing that 

 the season was not abnormal. 



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

 ratio of the lumen to the wall were measured both in sclerenchyma 

 and metaxylem elements. In the early stages the sclerenchyma 

 walls were thinner where potash had been supplied, but this effect 

 w as 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 

 |)otassic fertilisers 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 

 applied, 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, potassic fertilisers reduced the strength of mechanical 

 cells in the earlv stages of growth. I'his conclusion, however, 

 would ni^l h(»ld if potnssium sjilts affected the composition of the 

 wnll. 



From these results it is con»Muded that the rigidity of plants 

 supplied with potassium salts is not the result of anatomical 

 strengthening, but must be attributed to other causes, such as the 

 influence of the salts on the j^hv^if^lcigical condition of the plnnt, or 

 on its (liemical composition. 



y\\. R. A. FisHi'R. " Studies in Crop Variation. An 

 Examination of the Yields of Dressed Wheat from 

 Hroadbalk." Journal of Agricultural Science, 1921. 

 Vol. XI. 



A study of the variations in yield on Broadbalk where wheat 

 lias been grown continuously since 1843. 



Three types of variation are found due respectively to (1) 

 annual causes, primarily weather ; (2) steady deterioration of the 

 soil; (3) other slow changes, among which changes in weed flora 

 are considered. The effect of weather is reserved for further con- 

 sideration. The effects of soil deterioration and other slow changes 

 are studied at length. 



On the unmanured plot, the decrement in yield is of the order 

 of 0.8%, or less than 1 bushel in 10 years. If this rate were main- 

 tained, the plot would still last out another 125 years. Where 

 farmyard manure is applied there is practically no falling off in 

 yield ; this crop also shows the least variation due to weather. 

 With complete artificials, however, there is a deterioration, 

 but less with heavy than with light dressings of am- 

 monium salts, which is not quite in accordance with the Law 

 of Diminishing Returns. With incomplete artificials, however, 



