128 



Aluminium in certain Vascular Cryptogams. [Apr. 26, 



serve to some extent to neutralise the abundant organic acids of the 

 plants in which it occurs, and thus assist, like the cognate element 

 magnesium, in the metabolic processes of vegetation. 



One further observation may be hazarded. It remains to be seen 

 whether the study of the periodic function which connects the atomic 

 weights with the general properties of the elements will throw any 

 light upon the relations subsisting between vegetation and the few 

 elements necessary for its development. It seems that the position of 

 aluminium in Mendelejeff's third periodic series decidedly favours the 

 view of the peculiarity of its occurrence in certain plants, taken in 

 the present paper. It stands between magnesium and silicon, two 

 elements of which the physiological role is, to say the least, obscure ; 

 while of one of them — silicon, we may affirm that it is not an essential 

 plant-food. Its occurrence in the ashes of various plants is indeed 

 more general and more abundant than that of aluminium, but appears 

 to be quite as capricious ; and a point of difference as to the state in 

 which these two elements are found in plants is obvious. Aluminium 

 occurs mainly if not entirely in the form of soluble organic salts, 

 silicon in the form of insoluble silica. 



In considering this aspect of the periodic law one cannot help being 

 struck with the low atomic weights of the essential elements of plants. 

 If we exclude certain cases of apparently casual and accidental 

 absorption (of such elements as bromine, iodine, copper, zinc and 

 arsenic) it will be noticed that Mendelejeff's Series I, II, III and IV, 

 having a range of atomic weights from 1 to 56, comprise all the essen- 

 tial elements, even if we include manganese, chlorine, silicon and 



Elementary Plant-Food and the Periodic Law. 



Series I. 



Series II. 



Series IV. 





(Lithium 



7 



•0) 



Potassium = 



39 



1 





( Beryl limn ------ 



9 



•1) 



Calcium = 



40 









(Boron - 



11 



•0) 



(Scandium = 



44 



0) 





Carbon = 



12 



•o 



(Titanium = 



48 



•1) 





Nitrogen = 



14 







(Vanadium = 



51 



3) 





Oxygen = 



16 



•o 



(Chromium = 



52 



3) 





Fluorine = 



19 



•o 



Manganese = 



55 







Hydrogen = 1. 









Iron = 



56 









Sodium = 



23 















Magnesium = 



24 



•o 











Aluminium = 



27 



1 











Silicon = 



23 



3 











Phosphorus = 



31 



•o 











Sulphur = 



32 



•o 











Chlorine = 



35 



•5 









Series I. 



Series III. 





