SUPPLEMENT 21 



Since salts, as we now know, dissociate, at least partially, when in solution 

 in water, it is obviously a matter of indifference whether the base in the nitrate 

 be K or Ca, or that in the sulphate be Ca or Mg. In all probability salts which 

 do not dissociate are of no importance so far as absorption by the plant is 

 concerned, and hence the vital point only is that the kations K + , Ca ++ 

 Mg ++ , Fe ++ or F+++ and the anions SO 4 ~ and H 2 PO 4 ~ (as well as NO,-) 

 should be present. 



The reaction of the nutritive solution is, however, of great importance. 

 In alkaline fluids most plants die or at least suffer serious injury ; aquatic 

 plants are exceptional in this respect (MoLiscn, 1895-6 ; BENECKE, 1898), 

 for these forms thrive better in weak alkaline than in weak acid solutions. 

 In the case of all other plants a feebly acid reaction must be maintained in 

 the culture fluid. Under certain circumstances the reaction of the solution 

 may become alkaline by the more vigorous absorption of certain ions, and in 

 such cases it is advisable from time to time to add to the solution a few drops 

 of phosphoric acid, and so maintain a feeble acid reaction. More recently 

 CRONE (1904) has shown that neutral nutritive solutions are, under certain 

 circumstances, more favourable than acid ones; he also discovered that soluble 

 compounds of iron and of phosphoric acid are far less serviceable than those 

 which are sparingly soluble. The solution he used, and with which he obtained 

 satisfactory results, was composed of i g. KNO 3 0-5 g. MgSO 4 , 0-5 g. CaS0 4 , 

 0-25 g. Ca,(P0 4 ) 2 , 0-25 g. Fe ? (PO 4 ) 2 in 1,000 g. of 'water. 



It will be a valuable piece of work to invent a really scientific nutritive 

 solution, keeping in mind the poisonous effects of certain ions (of which we 

 shall speak later on) and their counteraction by other ions. 



In addition to the composition of the nutrient fluid and the reaction 

 dependent on it, its concentration and its amount are of primary import. 



82, 1. 4, for per cent, (bis) read per mille 



I. 14, after success read (NoBBE, 1864-68) 



II. 39-43, for The culture methods . . . improvement read Special care 

 must be taken to maintain purity in the salts used in cultures for lower plants 

 such as Algae and Fungi, because these organisms require extremely small 

 quantities of nutrient salts in accordance with their small size. Numerous 

 erroneous conclusions have been arrived at by neglecting the solubility of 

 glass vessels (compare BENECKE, 1896 and 1907). Apart from this, many 

 complications often occur in these plants as compared with higher types, 

 owing to the fact that Fungi, for instance, have quite special requirements, 

 inasmuch as, in addition to minerals, they also demand organic nutrients 

 (Lecture XIV). 



I. 48, for to the majority read occur in the majority - 



II. 53-4, for It has been shown . . . Algae require read On the other hand, 

 it has been shown by BENECKE (1894-1907) and MOLISCH (1895-6) that many 

 Fungi, Algae, and Bacteria require 



83, 11. 8-10, delete and on taking ... by the plant. 



I. 14, after globulins read and other compounds afterwards to be men- 

 tioned. 



II. 19-20, for nor . . . form read Fungi, however, grow well in the less 

 oxidized sulphur acids. Sulphur and phosphorus cannot, however, be used 

 in the elemental condition. 



11. 21-53, delete Further, sulphuric acid . . . without this element. 



84, 1. i, after unsuitable read to higher plants 



11. 7-34, for The case appears . . . may produce it. read In considering 

 the function of potassium in the higher plant it might be thought that it 

 would be easy to obtain definite knowledge on the subject by studying the 



