ASH. I 8i 



conditions from 60 to 370 times, and that buckwheat can increase 1,000 times 

 the weight of its seed ; an increase in dry weight of this amount may well be 

 described as abundant. Moreover, seedlings may show an increase in weight 

 without any absorption of ash constituents from the surroundings, and this is 

 explained quite simply by the not inconsiderable quantity of ash which the seeds 

 contain. Beans, for example, may, according to Boussingault, develop up 

 to the flowering stage entirely without nutritive salts and, in consequence, 

 double or quadruple their dry weight. We see from such illustrations that it is 

 necessary to eliminate the reserves in the seed entirely, if we desire to prove the 

 essential character of an element which may be present in small amounts in the 

 seed, but which amount may, for the purposes of development, be large enough. 



Without going into details we may mention only, with regard to the water- 

 culture method, that it is the custom, as a rule, to start from seeds which have 

 developed their principal roots in sawdust. The seedlings are then fixed in 

 the cork of a vessel of sufficient size, so that the stem is allowed to grow up- 

 wards and develop in light and air, while the root branches in the vessel contain- 

 ing the nutritive solution (Fig. 19). It is essential to prevent light from entering 

 the vessel, and this is done most effectively by sinking it in soil and at the 

 same time time keeping it at a uniform and not too high temperature. 



The following substances are employed as nutritive salts dissolved in water 

 so as to form a solution of a concentration of a few parts per thousand : 



The first of these nutritive solutions is the simplest, and with its aid Birner 

 and Lucanus were able to obtain a complete culture experiment with oats, 

 where the increase in dry weight was equivalent to 138 times the weight of the 

 seed. If we ignore for the present the nitrogen, which we will study later, 

 and which does not really belong to the ash constituents at all, we find that 

 the plant requires the following six elements : potassium, calcium, magnesium, 

 sulphur, phosphorus, iron. It can do without the other two elements, silicon 

 and manganese (which Salm-Horstmar believed to be essential), and also with- 

 out chlorine, as to whose indispensableness Salm was doubtful. All the six 

 elements first mentioned are absolutely essential, however, and if only one of them 

 be absent from the solution the increase in dry weight is greatly curtailed. In- 

 stead of increasing (in dry weight) from i to 138, the plant, in the absence 

 of magnesium, increases only to 5-1 ; without calcium, only to 1-3 ; without 

 potassium, only to 9-2 (compare Fig. 19, //) ; without iron only to 7-3 (in 

 another experiment only to 3-3) ; without phosphorus only to 6-5 ; without 

 sulphur only to 4-9 ; and only in a second experiment, where sulphur was 

 omitted, did the increase reach the relatively high figure of 35-4. 



Numberless experiments have been carried out with such nutritive solu- 

 tions, all giving the same or similar results. [Crone has obtained excellent 

 results with the following solution : potassium nitrate, i g. ; ferrous phosphate, 

 0-5 g.; gypsum, o-25g.; magnesium sulphate, 0-25 g.; made up to 1-2 lit. with water 

 (1904, Ergebnisse von Untersuch. iib. d. Wirkung der Phosphorsaure auf d. hohere 

 Pflanze, &c.. Diss. Bonn). Compare Benecke,i904 (Bot.Ztg.62, II Abt. p. 123).] 



It has been found best to keep the solution slightly acid ; if it be alkaline 

 it is apt to react injuriously on the plant, save in the case of aquatic plants 



JOST G 



