3^4 



LECTURE XVII. 



I assume the vessel in which the culture is made to have been first filled 

 with pure distilled water. In this case the seedling would nevertheless at first 

 grow vigorous and healthy, and, if w-e are dealing with large seeds of Beans or 

 Maize, 'produce three or four normal large leaves in the air, and several dozens 

 of lateral rootlets in the water. These organs arise and grow at the expense of 

 the materials — the so-called reserve materials — which were already present in the 

 seed. Soon, however, the moment arrives when these materials have disappeared 

 from their reservoirs, and are completely used up : there is then found in the 

 endosperm of the Maize seed, or in the thick cotyledons of the Bean, nothing 

 more of the starch and proteid matters previously abounding, and which in 

 these cases chiefly represent the nutritive materials reserved for the first stages 

 of germination. Microscopic examination would show 

 also that, in the roots, shoot-axes and leaves, the 

 stores of organic plastic materials are exhausted. 

 So far, therefore, the mere taking up of water by the 

 roots has sufficed for the construction of a number of 

 new plant organs, at the cost of the organic substance 

 stored up in the seed. The seed also contains a quan- 

 tity of mineral matters— compounds of potassium, mag- 

 nesium, calcium, iron, phosphorus, and sulphur. If 

 now the plants remain with their roots immersed in 

 distilled water, they hold out, it is true, for a long time, 

 but without growing at all considerably, and at last 

 they perish. 



If now several seedling plants of the same kind, e. g. 

 Maize or Bean, have been allowed to grow up to this 

 point, we may employ one or several of these indivi- 

 duals for the decisive experiment. We replace (which 

 of course is better done previously) the distilled water 

 by a solution of various salts, known to us from a long 

 series of earlier experiments. The simplest plan will 

 be to give here at once in a tabular form the salt 

 '" solution offered to the plants. I mention the quanti- 

 ties I am accustomed to use generally in water cultures, 

 with the remark, however, that a somewhat wide margin may be permitted 

 with respect to the quantities of the individual salts and the concentration of 

 the whole solution; it does not matter if a little more or less of the one or 

 the other salt is taken, if only the nutritive mixture is kept within certain limits 

 as to quality and quantity, which are established by experience. Thus the following 

 would be a useful solution : — 



Water . . ■ • 



Potassium nitrate .... 



Sodic chloride (common salt) 



Calcium sulphate (Gypsum) 



Magnesium sulphate 



Common calcic phosphate (finely pulverised) 



,000 cc.m. 

 I gramme. 

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