ACTION OF THE SALTS OF IRON ON VEGETATION 



469 



requires the employment of much feebler 

 solutions, in the proportion of one-fourth to 

 one-half a dram of the sulphate of iron to a 

 quart of water ; this solution may be ap- 

 plied, either partially or generally, by means 

 of a brush or sponge, to the upper or lower 

 surfaces of the leaves. If we experiment 

 more liberally, the excess of the solution 

 applied to the leaves, if allowed to moisten 

 the earth, may be absorbed by the roots. 



" A solution more concentrated, almost 

 always affects the leaves, and fixes brown 

 spots on them. 



" The action of the solutions is more or 

 less rapid, according to the nature of the 

 leaves and the permeability of the epider- 

 mis or outer surfaces, and, also, according 

 to the affinity or repulsive quality of the 

 surface of the leaves ; in which latter case 

 the absorption can only be effected by ren- 

 dering the liquid more viscid and conse- 

 quently more adhesive to these surfaces. 



" The soft leaves, like those of the scar- 

 let geranium, Pelargoniinn inqui7ians, the 

 primrose. Primula elatior, and artemesia, 

 Chrysa7ithemum indicum, are very sensi- 

 tive to the action of the Salts of Iron ; a 

 single application producing, at the end of 

 two or three days, a renewal of green to the 

 leaf wherever touched by the solution ; and, 

 in an example of a very chlorotic geranium, 

 every line painted on the surface of the leaf 

 by a brush was rendered beautifully distinct 

 through the intensity of the green color. 



" This action of v ry diluted solutions of 

 sulphate of iron on the chlorotic leaves of 

 plants, belonging to a large number of dif- 

 ferent families, as the vines and pears, which 

 are subject to this malady, is an unques- 

 tionable fact which M. Gris has sustained 

 by repeated proofs, and which your com- 

 missioners have confirmed on a great num- 

 ber of plants. 



" Here, none of the reactions peculiar to 

 the soil take place ; the solution is directly 

 absorbed by the organ which is to be modi- 

 fied ; it is absorbed like every other aqueous 

 solution ; if it be too concentrated , it changes 

 the tissue ; if it be weak, it acts favorably 

 on the diseased substance. It is to be farther 

 remarked, while the leaves are renewing 

 their color by the absorption of the Salts of 

 Iron through the roots, that the parts adja- 



cent to the nerves of the leaves are prima- 

 rily colored, and the networks of the leaves 

 secondarily, in the most distinct manner; 

 on the contrary, when the coloring of the 

 chlorotic leaves is the result of absorption 

 through their surfaces, the portions colored 

 are distributed in patches or spots bearing 

 no relation to the nerves of the leaves. 



" M. GoEPPERT had already observed si- 

 milar results in the poisoning of plants by 

 Prussic acid, acordingly as the impression 

 was produced by application to the roots, or 

 to the epidermis of the leaves in a state of 

 vapor. 



" It is quite important to demonstrate 

 the superiority of the action of the salts of 

 iron on vegetables, obtained by absorption 

 through the epidermis of the leaves, as this 

 method will be practically preferable to that 

 of absorption by the roots, especially for 

 trees, the absorbing extremities of whose 

 roots extend too far or almost beyond reach, 

 unless an enormous quantity of the solution 

 is employed ; whilst a weak solution, thrown 

 over the foliage by means of a syringe, will, 

 after two, three or four sprinklings, restore 

 the leaves to their normal state, by pro- 

 ducing, at first, green streaks, which gradu- 

 ally extend over the whole surface of the 

 leaf, with judicious and continued applica- 

 tions. 



" M. Gris assures us that he has derived 

 excellent results from this process applied 

 to very sickly chlorotic pear trees, (trained 

 en quenotiille ;) we have not had occasion to 

 test it on these trees. 



" It is moreover probable that the season, 

 during which the waterings, sprinklings or 

 lotions, are applied, has an important influ- 

 ence on their action ; for adult leaves, es- 

 pecially old and tough, appear to be less 

 sensitive to the influence of this agent, and 

 less susceptible of becoming green than 

 leaves still young and tender. 



" We have, also, already indicated the 

 great difference in the action, more or less 

 prompt and more or less marked, depend- 

 ing upon the texture «nd consistency of the 

 leaves themselves ; the leaves, with a very 

 penetrable covering or epidermis and 

 sponge tissue, almost immediately and with 

 facility experience the influence of the lo- 

 tions ; while others, on the contrary, with 



