STATE HOKTICULTURAL SOCIETY. 147 



But plants take other substances besides water from the soil. 

 Some of the absorbed materials are absolutely essential to the needs 

 of the plants, others appear to be more or less accidental. In the 

 first categor}^ are the salts of potash, lime, magnesia, iron and 

 phosphorus; in the second are silica, soda, manganese, etc. Among 

 the former must be some nitrates to supply the essential element, 

 nitrogen. 



The popular thought, too often founded on statements in books 

 of reputable authority, is that these soil elements are dissolved in 

 water, and that the solution is bodily sucked in by the plant. This 

 is far from fact. Analysis of the ashes of plants clearly show 

 that the substances are not absorbed in the proportions in which 

 they occur in the soil or in an aqueous solution. There is a large 

 quantity of common salt in sea water and the barest trace of iodine 

 and bromine; yet in the ashes of seaweeds proportionally large quan- 

 tities of the latter substances are found. Cabbages and beans, grown 

 side by side in gardens, take very different proportional amounts of 

 the solu))le soil elements. The truth is, these latter are taken mole- 

 cule by jnolecule, just as water is, and by reason of the same ever- 

 acting force — adhesion, or molecular attraction. When an amount 

 of any substance is taken sufficient to satisfy or equalize the attract- 

 ive affinity for that sul)stance no more is absorbed, unless in some 

 way the former amount is used u\) or changed to another state or 

 condition. For instance, the affinities of the plant substances for 

 sulphate of lime may be saturated. In this condition absorption 

 ceases. But in the physiological ])rocesses of the plant oxalic acid 

 is formed. Chemical action at once ensues between the latter and 

 the lime sulphate, and there results oxalate of lime, in the shape of 

 insoluble crystals, and free sulphuric acid, which is used as food. 

 Here, now, is an opportunity for the absorption of more lime sul- 

 phate, and the process may be repeated over and over again. But in 

 another species of plant no oxalic acid may be produced, hence no sul- 

 phate of lime absorbed beyond the first saturating amount. That 

 roots do, in some sense, select substances from the soil is uncjuestion- 

 able; that this selection is due to regular chemical and physical pro- 

 cesses may be regarded as equally certain. 



We have said tliat the chief function of roots is to absorb water 

 and other substances from the soil. Many go too far aiul impute to 

 them the office of directly using as food the absorbed materials, 

 and of as directly feeding the aerial parts of the plant. In the 

 division of labor existing in plants, it is the function of the leaves 

 to reorganize the elements absorbed by themselves and by the roots, 

 and to convert these materials into food proper. Plants can no more 

 live directly u])on carbonic acid and water, with a little potash and 

 lime intermixed, than can we ourselves. Under the stimulating 

 influence of the sun's rays the green parts of plants perform a 

 a most remarkable, as well as important and unique, office, called 



