THE ASH OP PLANTS. 145 



We easily see then, that, as circumstances are perpetual- 

 ly making new varieties, so analysis continually finds di- 

 versities of composition. 



9. Of all the parts of plants the seeds are the least liable 

 to vary in composition. Two varieties or two individuals 

 may differ enormously in their relative proportions of 

 foliage, stem, chaff, and seed ; but the seeds themselves 

 nearly agree. Thus, in the analyses of 67 specimens of 

 the wheat kernel, collated by the author, the extreme 

 percentages of ash were 1.35 and 3.13. In 60 specimens 

 out of the 67, the range of variation fell between 1.4 and 

 2.3 per cent. In 42 the range was from 1.7 to 2.1 per 

 cent, while the average of the whole was 2.1 per cent. 



In the stems or straw of the grains, the variation is much 

 more considerable. Wheat-straw ranges from 3.8 to 6.9 ; 

 pea-straw, from 6.5 to 9.4 per cent. In fleshy roots, the 

 variations are great ; thus turnips range from 6 to 21 per 

 cent. The extremest variations in ash-content are, how- 

 ever, found, in general, in the succulent foliage. Turnip 

 tops range from 10.7 to 19.7; potato tops vary from 11 to 

 near 20, and tobacco from 19 to 27 per cent. 



Wolff, (Die naturgesetzlichen Grundlagen des Acker- 

 baues, 3. Aufl., p. 117,) has deduced from a large number 

 of analyses the following averages for three important 

 classes of agricultural plants, viz.: 



Grain. Straw. 



Cereal crops 2 5.25 per cent. 



Leguminous crops 3 5 " " 



Oil-plants 4 4.5 " " 



More general averages are as follows, (Wolff loc. cit.) : 



Annual and biennial plants. 

 Seeds ... 3 per cent 

 Stems - - - - 5 " 

 Roots - - - 4 " " 

 Leaves - . - 15 " " 

 7 



Perenn ial plants. 

 Seeds - - - 3 per cent 

 Wood- - - - 1 " " 

 Bark - - - 7 " " 

 Leaves - - - 10 " " 



