I860.] 



THE SOUTHERN PLANTER. 



663 



form, the increased supply demands a 

 greater amount of water to carry on the f 

 functions of the plant in a healthy state. 

 Plants do not "burn" so readily on clay : 

 soils, which have the property of fixing the 

 ammonia in the soil, and only giving it up 

 more slowly to the plant, and thus prevent- * 

 ing all excess of nutriment. It seems, be- 

 sides, that Sacho and Stoeckhardt have 

 shown that the cereals and leguminous 

 grains, as well as clover and beets, not only 

 germinate, but attain a vigorous develop- 

 ment, and even blossom, although their 

 roots never come in contact with solid soil, 

 but merely float in water holding salts in 

 solution. 



If Brustlein would just consider what is 

 the chemical action involved in what he 

 terms "the choosing of food" by the roots 

 of plants, it might lead him to perceive that 

 the same force which enables the Duckweed 

 (Lemna trhulcd) to select the particular 

 kinds of food from solutions, might also 

 enable land-plants to take up readily sub- 

 stances that are little soluble in water. His 

 own experiments, indeed render the whole 

 subject much more easily apprehended. W. 

 S. Johnson, in attempting to explain the 

 selecting power exercised by the roots of 

 plants when growing in saline solutions, says: 

 But admitting that our analyses are suf- 

 ficiently accurate to base calculations upon, 

 and that the soil-water never contains more 

 potash, for example, than river and well 

 waters — viz. from 2 to 10 parts in 1,000,000 

 — it must be remembered that the plant is 

 by no means compelled to limit itself for its 

 supplies of mineral matter to the water 

 which it transpires. The root-cells of a 

 plant placed in a saline solution at once es- 

 tablish osmotic currents, in virtue of the 

 mutual but unbalanced attractions that exist 

 between the cell-walls, the liquid of the cell, 

 the surrounding liquid, and the saline and 

 organic mattets in solution in these liquids. 

 The assimilating processes going on in the 

 cells are constantly transporting matters for- 

 ward into the newer growths, or else remov- 

 ing them from solution in the sap, and caus- 

 ing their disposition in a solid form. . . 



. . As a result of this principle, the 

 land-plant collects the potash, phosphoric 

 acid, silica, &c, needed for its organization 

 from the recently dilute solutions of these 

 bodies, which form the water of wells or of 

 the soil, just as the fucus gathers its iodine 

 from the ocean. 



This explanation of the absorbing and 

 selecting functions of the roots of plants is 

 very much the same as that which he gave 

 in this Journal a few years ago.* We think, 

 however, that Johnson's is deficient in sim- 

 plicity, inasmuch as it introduces the 

 equivocal action of osmotic diffusion, and 

 which there is no occasion for taking into 

 account at all. Neither the iodine of the 

 ocean, nor the soluble food of plants in 

 waters of irrigation, is brought to them by 

 means of this power. Like the carbonic acid 

 in the atmosphere to the leaves of plants, 

 they are brought by currents; and as they 

 pass over living absorbing surfaces, are fixed 

 in the processes of assimilation. As we 

 have already said in the paper just referred 

 to— 



Leaves cannot be said to select the car- 

 bonic acid and ammonia of the atmosphere, 

 but they absorb these inorganic compounds 

 by virtue of certain affinites which exist be- 

 tween them under the influence of light. 

 The membrane which separates the cell-con- 

 tents in the spongioles of the roots of plants 

 from the inorganic world, is of a very deli- 

 cate character, and we can have no greater 

 difliculty in comprehending how it can ab- 

 sorb these inorganic substances, which may 

 have special affinites towards organic mat- 

 ters in the cell-membrane or cell-contents, 

 than that certain organic matters in the leaf 

 attract and absorb carbonic acid under the 

 influence of light. 



In the case of water-plants, there are al- 

 ways agents in operation which produce a 

 circulation of the solution among the roots. 

 In land-plants the roots are constantly ex- 

 tending and coming in contact with fresh 

 surfaces. Mr. Johnson considers that the 

 absorption of poisons is abnormal, whereas 

 we have always insisted that it is merely an 

 illustration of the power as it is active in 

 healthy absorption — chemical affinity. 



On the former supposition — that ammo- 

 nia, &c, existed in the soil as insoluble com- 

 pounds — to which we were led by the more 

 recent experiment of Way, Liebig, and 

 others, considerable difficulties were pre- 

 sented in accounting for the absorption of 

 nutritive substances. To these neither John- 

 son nor any other writer has alluded. If 

 these compounds really only entered into the 

 roots of plants by means of solutions, an ac- 

 ' tion must necessarily take place which 



* 1st October 1855. 



M 



