286 LECTURE XVII. 



and the plant which is supplied with a nutritive solution devoid of iron perishes 

 at length, simply because it is not able to form the proper organs of assimilation, 

 the chlorophyll-grains in the cells of the leaf, and when these are wanting the plant 

 is also unable to produce organic substances. 



It is quite unnecessary, and in no way advantageous, to leave the roots of the 

 experimental plants continually in the nutritive solution to which the iron has been 

 added ; experience shows rather that the plants flourish excellently if their roots are 

 placed now and again for a few days in pure water, or still better in an almost saturated 

 solution of gypsum. The roots, usually not perfectly healthy in the nutritive solution, 

 then grow again vigorously, and numerous new lateral roots are formed ; and when 

 this has happened the plant may again be placed in a new nutritive solution. We 

 may also proceed so that not all the salts given in the above table are simultaneously 

 presented to the roots; the salts may be distributed in two or three fractionated 

 solutions, and the plant allowed to absorb alternately the one or the other of them. 

 In this case also vigorous vegetation is maintained, and indeed I made the first 

 successful experiments on nutrition in this manner. 



The plants, then, being treated in the way described, new leaves and roots are 

 continually developed, flowers appear after six or eight weeks, and it is only necessary 

 to provide for the pollination of the female reproductive organ to produce fruit. 

 As a rule it sufiBces to let the plants stand at the open window or outside during 

 the time of flowering ; insects then provide for the transference of the pollen from 

 the anthers to the stigmas in the usual manner. The ovary then swells, and 

 after a few weeks a greater or less number of fruits are formed containing seeds 

 capable of germination. With the Maize, I have frequently obtained in this 

 manner heads of fruit with more than loo grains capable of germinating, and 

 with Beans 6-10 pods with 12-20 ripe seeds. If to the weight of these seeds 

 that of the organic substance of the shoots, leaves, and roots produced in our water- 

 culture is reckoned, it is shown that the organic substance, in comparison with that 

 of the seed from which the experimental plant was developed, may amount to three- 

 hundredfold and more. 



We have thiis by artificial nutrition raised a plant which has gone through 

 the whole course of its development, and we may employ its seeds for a second 

 experiment of the same kind. 



From this experiment it follows that the materials which we have placed at the 

 disposal of the plant completely suffice for the whole process of nutrition, and any 

 other addition of material is entirely superfluous. It should be mentioned here, 

 indeed, that the common salt specified in our table, or any other chlorine compound, 

 may be omitted, since numerous culture experiments have shown that sodium 

 and chlorine are, strictly speaking, superfluous in nutrition. On the other hand, 

 the presence of common salt or some other chloride is of use, in so far that the 

 nutritive solution can thereby be prevented from becoming alkaline'; since by 

 the absorption at the roots the chemical composition of the nutritive solution 

 becomes altered more and more in time. Of course this can also be avoided by 

 completely renewing the entire nutritive solution every three or four days. 



' Cf. Pfeffer, ' Pflanzenphysiologie! I. p. 254. 



