now PLA.NTS GROW. 163 



An artificial soil may be made up in just the right proportions of just the 

 right materials for any crop, and yet be absolutely sterile, because the materi- 

 als are not in a condition to be absorbed by tbe plant. 



The falsity of tbis notion need not seem strange to us after considering the 

 opening sentence in Johnson's Hoio Crops Feed, which reads: "A multitude 

 of observations has demonstrated that from 95 to 99 per cent of the entire 

 mass (weight) of agricultural plants is derived directly or indirectly from the 

 atmosphere." This does not, of course, mean that plants feed entirely upon 

 oxygen and nitrogen, the two chief ingredients of air, but that the air con- 

 tains nearly all, but not all, the other elements in sufficient quantity to sus- 

 tain plants. These are absorbed by rain and snow and dew, and brought 

 down to the plant. So much depends upon the degrees and variations of 

 moisture and heat and light, which are, at most, beyond our control; so little 

 is furnished by the soil, that it leaves a large element of uncertainty as to the 

 results after applying any particular fertilizer. 



Different varieties of the same species behave differently under the same treat- 

 ment. 



So much depending upon the weather, we see the need of a good knowlege 

 of meteorology as well as of chemistry and vegetable physiology. 



Time and space will allow me to merely quotq a table in Hoto Crops Feed, 

 page 98, giving the source of food to plants as taken from the atmosphere : 



Absorbed 



by 

 Plants. 



Oxygen, by roots, flowers, ripenins: fruit, and by all growing parts. 

 Carbonic acid, by foliage and green parts, but only in light. 

 Ammonia, as carbonate, by foliage, probably at all times. 

 Water, as liquid, through the roots. 



Nitric acid*^ \ United to ammonia, and dissolved in water through the roots. 



Ozone 



Marsh gas 



J- Uncertain. 



Notabsorbed]Sr''';^g«'^' , , 



{ Water m state of vapor. 



Exhaled Ozone? ' f ^^ foliage and green parts, but only in light. 



by 

 Plants. 



Marsh gas, in traces by aquatic plants. 



Water, as vapor, at all times. 



Carbonic acid, from growing plants at all times. 



Observe that buds, flowers, roots, ripening fruit, etc., give off and take in just 

 the reverse of green leaves in light. 



Although the air contains only 6 parts in 10 000 of carbonic acid, the air of 

 the soil contains 10 to 390 times that proportion. The composition of plants 

 changes with their growth. There is the greatest activity while flowering. 

 They take up different proportions of certain kinds of food at different times 

 during their growth. They require a change of diet. 



The seed of plants requires more of some kinds of nourishment than the 

 petals, stamens, or any other parts. For example: An analysis of the ash of 

 the oat-plant shows in the lower stem, of silica 14.1, middle 9.3, upper stem 

 20.4, lower leaves 34, upper leaves 41.8, ears 26.0, chaff 68, husk 74.1, kernel 

 1.8. In an analysis of eight parts of the plant (leaving out the seed) the lower 

 stem contains less silica. Seventy-five years ago, when silica was found in the 

 straw of wheat and oats, the conclusion was at once drawn that it serves to 

 stiffen the plant, and serve the purpose of bones in animals. 



Johnson says: "Two circumstances, however, embarrass the unqualified 

 acceptance of this notion." The proportion of silica is not greatest where most 



