364 The Physiology of Plants BOOK in 



tinues to grow the inner surface of the membrane remains 

 in close association with the salts. A further observation 

 on the growth of the pollen-tubes of Lilium confirmed 

 this view. Potassium can be detected at the moment the 

 tube emerges from the pollen-grain, and can be observed to 

 accompany its extension as it makes its way down the style. 

 Similar observations were made upon the conjugating 

 processes of Spirogyra, where the reaction of potassium 

 was given close to the terminal walls of the outgrowing 

 tubes. This reaction was found to be much more marked 

 than that of the adjacent cytoplasm, in which, as already 

 mentioned, the metal could be detected. 



The influence of calcium still remains obscure. Salm- 

 Horstmar proved it to be essential for the development of 

 Phanerogams, and Boehm associated it with the transport 

 of the reserve materials from the seed to the seedling. 

 In 1883 Raumer stated that from his observations he 

 concluded that the only special purpose it serves is to help 

 in the construction of the cell wall. Molisch supported 

 this view in 1895, by showing that the partial absence of 

 calcium causes an incomplete formation of the transverse 

 cell walls of Spirogyra. 



Stohmann found that in the case of maize in water 

 cultures, development ceased as the tissues became ex- 

 hausted of the metal, and that after several weeks, during 

 which growth was at a standstill, the addition of a calcium 

 salt was immediately followed by the growth of the buds. 

 In 1891 Palladin associated its presence with the proper 

 development of the leaves, and ascertained that etiolated 

 leaves contain only one-fifth the amount of the metal that 

 is found in normal ones. Schimper, in 1890, said that its 

 function is the neutralization of the oxalic acid and acid 

 oxalate of potassium in the tissues. In 1900 Loew 

 advanced the view that it enters into the composition of 

 certain protein compounds which are needed to supply 



