CHAPTER VIII. 



SOILS, ASH CONSTITUENTS, AND "WATER-CULTURE. 



632. When a plant is carefullj- dried at a temperature slightly 

 exceeding that of boiling water until it ceases to lose weight, 

 there remains behind a brittle combustible residue. The dif- 

 ference between the weight of the plant and that of the resi- 

 due represents the amount of water previously contained in 

 the plant. This differs widely, according to the kind of plant 

 and its age. The following table gives the proportion of water 

 contained in a few of the most common plants : — • 



Eed Clover, tefore flowering 83 per cent. 



" " in full flower 78 " 



Oats, before flowering 82 " 



" in flower 77 " 



Turnip (root) 91 " 



Beech (leaves), in summer 75 " 



" " in autumn 55 " 



Dry grains 14 to 15 " 



Dry woods 15 " 



633. If the brittle residue left after complete expulsion of the 

 water is burned in the open air, there remains beliind a small 

 amount of gray ash ; all the rest is wholly consumed. The 

 amount of ash also varies widely-, according to the kind of plant 

 and its age. In the following table ' are given the proportions 

 for a few common plants : — 



Per cent of ash in Per cent of aMi in 



fresli material. dry material. 



Red Clover 1.5 6.6 



Sugar Beet (root) .8 4.3 



Indian Corn 1.1 5.5 



" (grain) 2.1 1.5 



Beech (leaves), in summer ... 1.3 — 



" " in autumn ... 3. — 



634. In a general way it maj' be said that the combustible 

 matters are derived chieflj' from the atmosphere, while all the 



1 The student is referred, for detailed accounts of analyses from which these 

 figures have been chiefly taken, to Johnson's "How Crops Grow," 1868. 



