362 The Physiology of Plants BOOK in 



eluded either silicon or manganese, but they were in accord 

 with him as to the necessity of the other six. Calcium was 

 shown by Benecke in 1894-8 and by Molisch in 1895-6 

 to be unnecessary in the case of Fungi. 



The importance of sulphur and phosphorus became 

 evident when it was shown that these enter into the com- 

 position of the living substance. Boussingault in 1860, and 

 Lawes and Gilbert in the same year, showed that phosphates 

 play a part in the utilization of nitrates. In 1898 Macallum 

 showed by micro-chemical methods that phosphorus is an 

 integral constituent of the nucleus, and of the nucleolus. 



In 1862 Nobbe proved that the buckwheat produces no 

 fruit in the absence of chlorides, an observation confirmed 

 by Leydhecker in 1865 and 1866. In 1890 Aschoff found 

 that when these salts were not supplied to cultures of 

 beans and maize the terminal buds showed themselves 

 incapable of developing, and after a short time perished. 

 He noticed further that the leaves showed a great con- 

 gestion of starch grains. Aschoff could not, however, assign 

 any specialized function to the chlorine. 



Silica was investigated in 1883 by Kreuzhage and Wolff ; 



they found it to be necessary for the full development of 



"the cereal grasses, aiding in the utilization of the other 



nutrients and leading to a better production of seed and 



to an earlier ripening of the grain. 



Potassium was the subject of much research. In 1871 

 Nobbe, Schroeder and Erdmann found that in its absence 

 the chloroplasts fail to form starch. They further noticed 

 that unless the form in which it was supplied is the 

 chloride, there is a great congestion of starch grains 

 in the leaf. In the light of Aschoffs work already men- 

 tioned the latter peculiarity may be associated with the 

 absence of the chlorine. 



In 1887 Lupke found that the absence of potassium does 

 not interfere with the development of any of the different 



