CHLOROSIS. 



285 



The calcium phosphate, last mentioned, is but sparingly soluble in the solution 

 and forms a sediment during the course of the experiment. 



The result of this proceeding becomes evident after a few days, in that the 

 plants appear more vigorous as contrasted with those the roots of which have 

 remained in pure water, and in that new lateral roots grow from their roots, and 

 new leaves from their buds. After some time, however, when the third or fourth 

 leaf of our experimental plant is unfolding, a diseased condition appears. The 

 new leaves which develope henceforth remain completely white, that is, they 

 produce no chlorophyll ; and microscopical investigation shows, as Gris first 

 observed in similar cases, that no chlorophyll grains are present in the protoplasm 

 of such colourless leaves. This then is a proof that our mixture of nutritive 

 materials still lacks something, and from the older observations of Gris, we 

 know that the disease of our plants — so-called Chlorosis — is due to a want of 

 iron'. Our experiment has thus taught us at the same time how this disease 

 (which occurs not rarely also under ordinary conditions of growth, e. g. in Robinias, 

 Horse-chestnuts, and other plants) may be produced artificially. However, the 

 curing of this disease may also be efi"ected at once : it suffices to add an 

 extremely small quantity of a soluble salt of iron, e. g. a few drops of solution of 

 iron chloride or ferrous sulphate, to the water which the roots take up, in order 

 even after forty-eight hours (or, according to circumstances, after three or four 

 days) to see the white leaves of the Bean or Maize becoming green : after 

 several days they are quite normally green. The action of the iron on the 

 formation of chlorophyll may be demonstrated even more simply; if a very 

 dilute solution of a salt of iron is painted with a camel-hair pencil on the 

 surface of a chlorotic leaf, the formation of chlorophyll in the leaf begins at 

 this place after one or two days, and gradually extends thence. It may here 

 be mentioned that I made auger-holes in the stem of an Acacia, the foliage 

 of which was completely chlorotic, and placed funnels, filled with solutions of 

 iron, in the holes ; the solution of iron carried up from the auger-hole through 

 the wood into the leaves of the next branch, in a few days caused the leaves 

 of this branch to become completely green, while the others remained chlorotic. 

 These experiments evidently prove that iron is necessary for the formation of 

 chlorophyll, but they do not show whether the iron forms a constituent of the 

 green colouring matter itself: it is possible, according to recent statements, that 

 the latter is actually the case. It must be mentioned further that only an ex- 

 tremely small quantity of iron is necessary : several milligrammes of a soluble 

 iron salt per litre of nutritive fluid are quite sufficient to remove the chlorosis 

 of the plant under experiment, and larger quantities of iron act as a poison 

 on the roots as well as on the leaves. At the same time, however, the course 

 of our experiment shows how important these small quantities of iron are for 

 the total life of the plant: since if they are withheld the white chlorotic leaves 

 perish after a time. The feeble nutrition by means of the first two or three 

 green leaves of the plant does not suffice to bring about any considerable growth ; 



* The literature of these and other facts appertaining here is quoted in my ' Expcrimeiiial- 

 physiologie^ 1S65, p. 141, &c. 



