BONE MANURES 177 



a large portion of his calculations must be left to chance. 

 The maximum utilization of any fertilizing ingredient can 

 only take place when everything is favourable. Hence it 

 may happen that the greatest need of a fertilizing material 

 will occur in one case during the early stages of growth 

 of the plant, on another occasion during the main period of 

 plant growth, while the critical point in the history of a third 

 plant may be its ripening period. For the purpose of 

 promoting germination of a seed, readily soluble constituents 

 are absolutely essential. Very considerable acceleration 

 in the rate of germination of seed can be produced by very 

 weak solutions of various salts. Highly soluble materials 

 are therefore very efficacious at that period of growth. For 

 later periods of growth, root stimulation is desirable, and 

 roots do best if they have to travel some little distance to 

 find their food ; the encouragement of a mat of roots close 

 to the stem is undesirable, and likely to produce serious 

 difficulty should drought intervene. There is consequently 

 a great advantage in having fertilizing ingredients in several 

 different forms in the fertilizing mixture used, but to obtain 

 that end by treating bones with sulphuric acid is an unneces- 

 sarily expensive process. The same results can be obtained * 

 much more economically by mixing superphosphate, bone 

 meal, perhaps a little rock phosphate, sulphate of ammonia 

 and other ingredients. Steamed bone flour is a particularly 

 convenient article for making a mixture, since it dries up 

 the superphosphate with which it is mixed. As described 

 in the article on Superphosphate (p. 151), there are diffi- 

 (fulties in making a dry superphosphate, even under the best 

 conditions ; the power to be able to add a really useful 

 drying material like steamed bone flour is very valuable. 

 Superphosphates which are difficult to obtain in a dry con- 

 dition may even be hurried through the den, and then 

 subsequently dried by admixture with bone meal. This 

 method provides an economical system of obtaining a bone 

 compound containing at least two kinds of phosphate and 

 one kind of nitrogen. The composition of any such bone 

 compound is just exactly what the manufacturer desires, 

 v. 12 



