22 PLANT PHYSIOLOGY 



effect of a normal water-culture solution containing no potassium. As a matter 

 of fact, however, the results of such studies, e.g. those of SCHIMPER (1890) 

 and of WILFARTH and WIMMER (1903), are so divergent that it is impossible to 

 draw any certain conclusions from them. In other cases also, e.g. in relation 

 to phosphorus and calcium, the effects of water-cultures which do not contain 

 these elements are ambiguous. Of one reason for that we shall speak later ; 

 at present we must content ourselves with assuming that potassium is a con- 

 stituent of protoplasm and hence is an essential nutrient. Most proteid bodies, 

 as a matter of fact, contain ash, and it is quite possible that these bodies, at 

 least in part, are directly concerned in the building up of the proteid molecule. 



The lower plants behave quite otherwise in their demand for metals of 

 the alkalis. Replacement of K by Na, Li, and NH 4 is generally ineffectual, 

 and it is only in the case of the Cyanophyceae perhaps (BENECKE, 1898, p. 96) 

 that Na may replace K. On the other hand, according to BENECKE (1907), 

 certain Bacteria can live perfectly well without K, when presented with Ru 

 or Cs salts in proper concentrations. Many Mould Fungi behave in the same 

 way, for in their case Ru or Cs suffices for the formation at least of vegetative 

 organs. Since, however, reproductive organs are not formed under these 

 conditions, it would appear that K is as essential to them as it is to higher 

 plants. 



11. 37-8, delete Water-cultures . . . potassium. 



11. 43-4, for Magnesium . . . chlorophyll read Magnesium also appears to 

 be plentifully present in chlorophyll. 



1. 45-9, for Though most Algae . . . contain it. read Since most lower 

 organisms can do without it we must conclude that it is not an essential con- 

 stituent of the proteids of protoplasm, although, it is true, differences may 

 occur even in the most important chemical compounds in individual groups 

 of plants. 



I. 54 P. 85, 1. 16, for The appearance ... for calcium, strontium would 

 read Why it is essential and what its function is, we do not know. Were 

 it possible to replace it by another metal, strontium would 



85, 1. 24, for as a consequence of read after 



II. 47-50, for MOLISCH (1892) . . . same fact, read MOLISCH (1892) and 

 by WILLSTATTER (1906), who found that chlorophyll contained no iron. On 

 the other hand, an older research of RAULIN'S (1869), showing that Fungi 

 which have no chlorophyll cannot do without iron, has been confirmed by 

 MOLISCH (1892) and BENECKE (1895). 



1- 53, after effect, read Whether chlorosis is always to be regarded as an 

 indication that iron is absent from the nutritive solution or that the plant 

 has not access to it, is a question we must leave undecided. Doubtless, other 

 differences in the nutritive solution may also induce chlorosis. 



86, 11. 3-5, for hence it should . . . discussed here, read hence nitric acid, 

 as an essential nutrient, capable of being absorbed from the soil or from water, 

 must be referred to in this connexion, although, not being found in the ash of 

 plants, it should not, strictly speaking, be discussed here. 



1. 32 P. 89, 1. 4, for In addition to ... the subject intelligible, read In 

 addition to the six elements spoken of above as essential to all higher plants, 

 there are others which, although they are absorbed in large quantities by 

 plants growing in the open, are yet to be regarded as unessential. Sodium is 

 the best example of these. Although in almost all the analyses given in the 

 table on p. 80 it is present in greater amount than the essential constituent 

 iron, still, with the aid of the water-culture method, it may be shown to be 

 quite unessential, although it must not be assumed that it is, if offered, quite 

 useless. For certain general purposes, e.g. neutralization of acids or osmotic 



