AGRICULTURAL CHEMISTRY. 131 



Other experiments proved that eJdorine is essential to the growth 

 of wheat. 



Wiegmann and Polstorff found that when seeds of cress (Lepidium 

 sativum) were sown in minced platinum wire, contained in a platinum 

 crucible, and moistened with distilled water, the experiment being 

 conducted under a glass shade, out of reach of dust, they germinated 

 and grew naturally during twenty-six days, when, having reached a 

 height of three inches, they began to turn yellow and to die down. 

 On burning the plants thus produced, their ash was found to weigh 

 exactly as much as was obtained from a number of seeds equal to that 

 sown. Prince Salm Horstmar found that oats grown with addition 

 of fixed mineral matters (ash ingredients) only, gave four times the 

 mass of vegetable matter that was obtained when these were withheld. 



The plant, as we have seen, is an assemblage of cells, which are 

 situated in more or less close contact with each other. The plants 

 that consist of but a few cells, like yeast, simply lie or float in the 

 medium in which they are naturally found. Agricultural plants, how- 

 ever, and the higher orders generally, possess roots, whose functions 

 are performed underground, and stems, leaves, and flowers, that exist 

 in the air. 



The yeast plant finds its food in the fermenting solution, and the 

 cells have a power of absorbing their nutriment out of this solution. 



Marine plants wholly immersed in the ocean abstract their food 

 from the sea water. 



The higher land plants' derive the materials from which their cells 

 are multiplied, partly from the soil, by their roots, and partly from the 

 atmosphere, by their foliage. 



In the living plant, then, there is provision for the access of liquids 

 into the cells from without, and for the transmission of the same from 

 one end of the plant to the other, or in any direction: for if we plant 

 a seed in pure sand mingled with ashes and duly watered, we shall 

 find in a few weeks that a plant has resulted containing in every por- 

 tion of it carbon, hydrogen and nitrogen, which could only have been 

 derived from the atmosphere, and also saline and earthy matters, which 

 must have been imbibed from the ashes and carried upward to the 

 points of its branches and leaves. 



The young cell, though its wall reveals no perforation to the most 

 powerful magnifier, is porous: and though the older cells, which form 

 the cuticle of a somewhat developed plant, are often impermeable to 

 water and air. from the fact that they are indurated or glazed by the 

 formation of a corky or waxy coating, yet the young cells that are 

 continually forming at the extremities of the advancing rootlets, and 

 those of the still fresh leaves, are highly porous, and no more oppose 

 resistance to the passage of water or of air than does a sieve. 



We have only to immerse the roots of a vigorous plant in a solution 

 colored with some harmless pigment, and in a short time we can trace 

 its diffusion throughout the plant. 



If liquids thus easily permeate these tissues, there is every reason 

 to suppose that they may admit the vastly more subtle particles of a 

 gas: and of this we have abundant experimental evidence, as will be 

 set forth bye and bve. 



