254 WATER-CULTURE. 



679. Iron. 1 When a plant is provided with a nutrient solu- 

 tion containing all essential elements except iron, its ehloroplvyll- 

 granules fail to attain complete development. The}" remain in 

 an imperfect condition, and do not have the characteristic green 

 color. Upon the addition of a mere trace of a salt of iron to the 

 solution a change is observable at once, the granules assuming 

 their proper shape and color. Plants grown in a solution with- 

 out iron have a pale and even blanched look, which at once 

 disappears when iron is added ; moreover, a local effect is pro- 

 duced when a solution of a salt of iron is placed on the surface 

 of the blanched leaves of such plants, - - a green color is given 

 wherever it touches. But it must not be supposed that the fail- 

 ure of some leaves to produce chlorophyll at certain points or 

 spots is always due to absence of iron. 



It is not clear that iron, which is so necessary to the produc- 

 tion of chlorophyll, enters into the composition of either the 

 granule or the pigment ; but according to Pfeffer there is a 

 strong probability that in the latter it exists in the form of some 

 organic compound. Iron has been found in the cell-walls of cer- 

 tain algae 2 (as an incrustation), and also in the fruit of Trapa 

 natans, the frond of Lemna trisulca, and sparingly in other 

 plants, as shown by the analyses collated by Wolff. 



680. Chlorine. This element appears, from experiments by 

 Nobbe 3 and Beyer, 4 to be indispensable to the full development 

 of some plants (e. g., buckwheat), but it is not required for many 

 others (e. g., Indian corn). 5 Nobbe concludes, from his experi- 



would otherwise be the case. In the life of the plant this work of the alkaline 

 phosphates plays a very important role " (Physik der Pflanze, 1867, p. 129). 



1 That iron is indispensable to the full vigor of plants was shown by Eusebe 

 Gris in 1843, and the subject was further studied by Arthur Gris in 1857. 

 Salm-Horstmar (in 1856), Sachs, and others have added much to the knowledge 

 of the subject, showing that no other element can replace iron in producing 

 the changes noted above. 



2 Colin : Beitrage zur Biologie der Pflanzen, 1870, p. 119. 



3 Versuchs-Stationen, vii., 1865, p. 371 ; xiii., 1870, p. 394. 



4 Versuchs-Stationen, xi., 1869, p. 262. 



5 Knop : quoted by P fetter, PHanzenphysiologie, i., p. 259. 



The conclusions reached by Johnson in 1868 appear to need little modifica- 

 tion at the present date. " 1. Chlorine is never totally absent. 2. If indis- 

 pensable, but a minute amount is requisite in the case of the cereals and clover. 

 3. Buckwheat, vetches, and perhaps peas, require a not inconsiderable amount 

 of chlorine for full development. 4. The foliage and succulent parts may 

 include a considerable quantity of chlorine that is not indispensable to the life 

 f the plant" (How Crops Grow, p. 182). 



