SECTIONAL TRANSACTIONS.— M. 419 



tissues. The rule is general and applies to any soluble salt added to the medium in 

 which a plant is growing. Up to a certain point the uptake is proportional to the 

 -amount supplied ; beyond that it falls ofi. 



The additional nutrient may cause an increase in growth but not a strictly 

 proportional increase. For small increments of the nutrient the growth may be lees 

 than proportional and for larger increments more than proportional ; for still larger 

 increments it is again less than proportional and beyond a certain point ceases alto- 

 gether. The curve is sigmoid, but it may be nearly logarithmic. 



In consequence, the first increment of added fertiliser to a crop insufiBciently 

 supplied with the particular nutrient may cause an increase in the amount of the 

 nutrient ion in the plant without correspondingly increasing the amount of growth. 

 The percentage of the ion in the dry matter of the plant therefore increases. Further 

 increments of the fertiliser may cause an increase in growth proportional to the added 

 fertihser so that there is no change in the percentage of the nutrient ion in the dry 

 matter. Still further increments cause little or no further growth : the effect on 

 composition depends on whether uptake of the nutrient ion still continues. Uptake 

 of nitrogen and of potassium goes further than that of phosphorus. Instances are 

 given showing how dressings of phosphatic fertihser to soils deficient in phosphate 

 increase the phosphorus content of the crop, but when larger quantities of phosphate 

 are present in the soil dressings of phosphatic fertiliser cause no further increase. 

 Dressings of nitrogenous fertiliser, however, continue to increase the nitrogen content 

 of the crop. 



The ions entering the plant are not necessarily linked with any particular ion and 

 in consequence the additional uptake of any one ion increases its amount relative to 

 the others so reducing their percentage amounts in the dry matter or ash of the plant. 

 Thus, addition of nitrogenous or potassic fertilisers lowers the percentage of phosphorus 

 in the crop. These variations in composition are greatly damped down in the matura- 

 tion process : the grain reflects them only feebly : its composition is determined 

 mainly by temperature and water supply at the various stages of growth, in other 

 words — the weather. 



Excess of any particular nutrient ion in the plant causes characteristic disturbances 

 in its structure and behaviour. These are specially clearly marked for nitrogen ; 

 apparently the plant functions normally only within a certain range of values for the 



ratio — . These disturbances are most easily counteracted by increasing the supply 



of potassium, which increases the efiSciency of the leaf as a producer of carbohydrate 



C K 



and therefore restores the ^=^ ratio to more normal values ; hence, in practice, the — 

 _ _ N N 



ratio is useful to the expert adviser. 



Deficiencies of the various nutrients also cause well marked disturbances, the 

 recognition of which is useful to the agricultural expert as a means of diagnosing 

 serious but not slight soil deficiencies. It is not always possible to separate these 

 •deficiency effects from the effects of the relative excess of some other nutrient. 



(6) Dr. L. R. Bishop. — Barley. 



On English arable soils the only fertiliser causing important increases in yield is 

 nitrogen. One hundred-weight of sulphate of ammonia per acre gives an increased 

 yield of approximately six bushels of grain. It does this without marked effects on 

 the composition and ' quality,' since the extra nitrogen absorbed from the manure is 

 approximately balanced by the resulting extra carbohydrate. Potash and phosphate 

 fertilisers have no appreciable effects on barley composition on Enghsh arable soils 

 and only on certain deficient soils do these manures increase the yield noticeably. 

 Heavy doses or late top dressings of nitrogenous fertilisers raise the nitrogen percentage 

 of the grain since they do not produce a proportional increase in carbohydrate 

 production. 



The important nitrogenous constituents have been studied in detail and it is con- 

 ■cluded that the amount of each of the separate proteins in the mature grain is regularly 

 and solely related to the total nitrogen content of the grain in a way which is charac- 

 teristic of each variety. The protein amounts are thus uninfluenced by the manuring 

 or by soil or season. The amount of gluteUn is directly proportional to the total nitrogen 

 -content. With increasing total nitrogen the hordein increases more rapidly and the 



EE 2 



