SUPPLEMENT 39 



have shown that ammonia is almost as good, and in some cases even a better 

 nutrient than nitric acid. TREBOUX (1904) claims that ammonia quite gener- 

 ally leads to more favourable results, but he has not as yet furnished us with 

 any evidence in support of his view. In cases where the results obtained with 

 ammonia are poor, we may often put it down to the inability of the root to 

 endure the presence of salts of ammonia in higher concentration. The poisonous 

 effect of ammonium carbonate, coincident with its alkaline reaction, has been 

 noted, while, on the other hand, a | per cent, solution of ammonium sulphate 

 appears to have no evil effect at all. 



Nitrites may be regarded as third in series, for MOLISCH (1887) has shown 

 that in weaker concentrations they are plentifully absorbed, and are reduced 

 in the plant, while in stronger doses they are markedly toxic. According to 

 TREBOUX (1904) this toxic action disappears when the solution is alkaline, 

 and then the nitrites are even better nutrients than the nitrates. This wants 

 confirmation, however. 



Finally, there are the humin substances to take account of, for they 

 always contain abundant nitrogen, and are widely distributed in nature ; 

 that their nitrogenous constituents are, at least partly, made use of by the 

 higher plants is not improbable but not definitely proved (NiKixiNSKi, 

 1902). 



136, 1. 15, after itself, read In the tropics the amount of combined nitrogen 

 present in rain is much greater than it is in our country ; MUNTZ and MARCANO 

 found as much as 16 mg. per litre at Caracas. 



11. 18-19 f or t m tropical . . . 1889)] read in tropical countries as much as 

 6kg., 



1. 24, for in general read at least in part, 



I. 25, for XVII). This substance is greedily read XVII) ; the remainder 

 appears in the almost insoluble humin substances. Ammonia is greedily 



II. 29-30, delete In this way . . . ammonia. 



1. 50, for This evolution read A loss of this kind never occurs in the higher 

 plant (CASTORO, 1904), for the plant is altogether more economical of its 

 nitrogen than the animal ; on the other hand, an evolution 



137, 11. 10-12, delete Without doubt . . . soil. 



I. 32, after soil, read We have now to investigate the amount of 

 nitrogen present in the soil, and in the first place that present in uncultivated 

 land. 



138, 1. 2, after in it. read We can scarcely go far wrong if we assume 

 that the nitrogen is very frequently the limiting factor, and that on the 

 amount of that element depends chiefly the amount of plant production in 

 nature. 



II. 5-6, for Just as ... removed, read For precisely the same reasons brought 

 forward when speaking of the materials of the ash, so here also agricultural 

 success depends on how much overcropping takes place so far as nitrogen is 

 concerned. 



I. 9, for is read are 



II. 22-3, delete traceable in its origin to vital activity. 



11. 26-30, for [Probably . . . detail later, read Further, those plants which 

 fix the nitrogen of the air are of the greatest importance in agriculture, but of 

 them we shall treat later (Lecture XIX). At present it must be noted that 

 the artificial combination of atmospheric nitrogen has been accomplished, 

 and the product, calcium cyanamide (CaCN 2 ), has been added to the soil as 

 a substitute for other nitrogenous manures, where it undergoes decomposition 



