668 PROCEEDINGS OF SECTION K. 



The most striking results appear to be due to the use of two of 

 these rare elements at the same time. It may be asked whether 

 mora striking results could be obtained by using three or more 

 of these elements. If, as it seems likely, these elements are, in 

 some cases at least, a condition of life of a given vegetable, their 

 addition to the growing medium would not fail to give satisfactory 

 results. 



On the other side, there are a certain number of experiments 

 in which the same elements have proved either ineffective, or in 

 varying degree harmful to the plant. The question, conse- 

 quently, deserves to be gone into to see whether in the light of 

 what has already been done, some conclusions can be drawn, 

 though without doubt, long study and experiments will be required 

 to throw complete light on this complex and greatly important 

 problem. 



Those who admit that the beneficial effects realized have been 

 really caused by these elements, be it Mn, or Zn, or B, or any 

 other of these catalytic agents, consider these elements to be in- 

 dispensable to the development and growth of the plant. To take 

 a single example — Duclaux in his Traite de Microbiologie, speak- 

 ing about the growth of Aspergillus niger in presence of zinc, defi- 

 nitively states that without zinc this mould cannot exist. 



It would follow from this that different plants require different 

 foods, contradicting the popular view that some elements only, as 

 C, N, P, K, are necessary to vegetable life. It v/ould be better 

 to say that these elements are found in all plants, and other 

 elements are required by this or that other vegetable. In such 

 a way we could explain how, in some cases, the addition to the 

 growing medium of some of these rare elements has proved ineffec- 

 tive and even harmful to the plant. Examples could be given 

 of harmful effects brought about by the use of some of the 

 elements which are reputed essential constituents of plants. 



According to Burman {Bull. Soc. Chitn., 1911, iv. 9., 957-959), 

 Digitalis purpurea can only be grown in the garden, and in pre- 

 sence of manganese. The ash of this plant contains 9.02 per cent, 

 of Mn. The presence of Mn. in the ash serves to distinguish 

 Digitalis purpurea from D. a/nhigua and D. lutea. 



Ivy, according to W. von Klenke (Zeit. Landw. Vers. West 

 Oesterr 3, 629-630) is a calcareous plant. Its ash contains 31.09 

 oer cent, of lime. 



Henry G. Smith (J. Roy. Soc. N.S.W., 1904. 37, lOJ-120) 

 found from 36 to 43, and even 79.66 per cent, of alumina in the 

 ash of the peripheric part of Orites Excelsa. 



U. Suzuki {Bull. Coll. Agr. Tokyo Imp. Univ., 1901, J^, 

 418-440) found 12.1 and 12 per cent, of FejOg in the ash of the 

 seed of Peligonium tinctorium and of Indigotifera tinctoria. 



