172 HOW CEOPS GROW. 



renewed, barley made no progress beyond germination, and 

 a buckwheat plant, which at first grew rapidly, was soon 

 arrested in its development, and yielded but a few ripe 

 seeds, and but 1.746 grm. of total dry matter. 



While water-culture does not provide aU the normal 

 conditions of growth — the soil having important func- 

 tions that cannot be enacted by any liquid medium — it 

 is a method of producing highly-developed plants, under 

 circumstances which admit of accurate control and great 

 variety of alteration, and is, therefore, of the utmost value 

 in vegetable physiology. It has taught important facts 

 which no other means of study could reveal, and promises 

 to enrich our knowledge in a still more eminent degree. 



Potash, Lime, Magnesia, Phosphoric Acid, and Sul- 

 phuric Acid, are absolutely necessary for the life of 

 Agricultural Plants, as is demonstrated by all the experi- 

 ments hitherto made for studying their influence. 



It is not needful to recount here the evidence to this 

 effect that is furnished by the investigations of Salm- 

 Horstmar, Sachs, Knop, and others. (See, especially, 

 Birner & Lucanus, Vs. St., VHI, 128-161.) 



Is Soda Essential for Agricultural Plants ? This 

 question has occasioned much discussion. A glance at 

 the table of ash-analyses, (pp. 150-56,) will show that the 

 range of variation is very great as regards this alkali. 

 Among the older analysts, Bichou found in the ash of 

 the pea 13, in that of the bean 19, in that of rye 19, in that 

 of wheat 27 per cent of soda. Herapath found 15 per cent 

 of this substance in wheat-ash, and 20 per cent in ash of 

 rye. Brewer found 13 per cent in the ash of maize. In a 

 few other analyses of the grains, we find similar high per- 

 centages. In most of the analyses, however, soda is pres- 

 ent in much smaller quantity. The average in the ashes 

 of the grains is less than 3 per cent, and in not a few of 

 the analyses it is entirely/ wanting. 



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