172 HOW CROPs GROW. 
renewed, varley made no progress beyond ge mination, 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 all the normal 
conditions of growth—the soil having important fune- 
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. S¢., VIII, 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, Bichon found in the ash of 
the pea 13, in that of the bean i9, in that of rye 19, in that 
of wheat 27 per cent of soda. HUcrapath 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. Ina 
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. 
