163 HOW CROPS GROW. 



of asli-ingredients occurring in plants. . This point will 

 shortly be discussed in full. By taking the ayerage of 

 many trustworthy ash-analyses we arrive at a result which 

 does not differ very widely from the majority of the in- 

 dividual analyses. This is especially true of the seeds of 

 plants, which attain nearly the same development under 

 all ordinary circumstances. It is less true of foliage and 

 roots, whose dimensions and character vary to a gre^t 

 extent. In the following tables (p. 164-170) is stated the 

 composition of the ashes of a number of agricultural 

 products which haye been repeatedly subjected to analy- 

 sis. In most cases, instead of quoting all the individual 

 analyses, a series of averages is given. Of these, the first 

 is the mean of all the analyses on record or obtainable by 

 the writer,* while the subsequent ones represent either 

 the results obtained in the examination of a number of 

 samples by one analyst, or are the means of several single 

 analyses. In this way, it is believed, the real Tariations 

 of composition are pretty truly exhibited, independently 

 of the errors of analysis. 



The lowest and highest percentages are likewise given. 

 These are doubtless in many cases exaggerated by errors of 

 analysis, or by impurity of the material analyzed. Chlo- 

 rine and sulphuric acid are for the most part too low, be- 

 cause they are liable to be dissipated in combustion, while 

 silica is often too high, from the fact of sand and soil ad- 

 hering to the plant. 



In two cases, single and doubtless incorrect analyses by 

 Bichon, which give exceptionally large quantities of soda, 

 are cited separately. 



A number of analyses that came to notice after making 

 out the averages are given as additional. 



* At the time of preparing the first edition of this book, in 1868. More 

 recent analyses are comparatively few in numher, excepting those of 

 wheat (grain and straw) by Lawes Sl Gilbert, and do not difier essen- 

 tially from those given. The numerous very incorrect ash-analyses, 

 published by Dr. B. Emmons and Dr. J. H. Salisbury, in the Natural 

 History of New York, and in the Trans, of the New York State Agricul- 

 tural Society, are not included. 



