528 The Philippine Journal of Science 1920 
the form of the salts monopotassium phosphate, calcium nitrate, 
magnesium sulphate, and ferric phosphate. Oat plants grown 
in solutions that lacked any of these elements were found to 
have much smaller dry weights than those grown in the full 
nutrient solution. Similar experiments by later workers with 
many other kinds of higher plants have given the same general 
results; namely, that the dry yield is much greater when all 
seven of these elements are present in the culture solution than 
when one or more of them are omitted. 
Birner and Lucanus also showed that these seven are the 
only elements that are necessary for excellent growth of oat 
plants. There has been considerable discussion, however, among 
various writers as to whether certain other elements may not 
be essential for plants in general or for certain plants in 
particular. Nobbe and others, for example, believed that chlor- 
ine was necessary for the complete development of the buck- 
wheat plant. 3 Beyer 4 reported that the fruiting of oats and 
peas was not normal in culture solutions that lacked chlorine. 
Also, Salm-Horstmar 5 6 was of the opinion that silicon and man- 
ganese were necessary for oats. But from all the work that 
has been done it may be concluded that for most higher plants 
only the seven elements mentioned above are to be regarded as 
essential constituents of the nutrient solution. 
There still remains, however, the problem as to whether plant 
growth may not be significantly accelerated in the presence of 
nonessential elements, and modern investigators have studied 
the effects of a number of such elements. Of course it is well 
known that many unnecessary elements act as poisons and re- 
tard plant growth when supplied in certain concentrations, and 
the problem thus suggested has also been taken up by many 
writers. 
3 Nobbe, F., and Siegert, T., Ueber das Chlor als specifischen Nahrstoff 
der Buchweizenpflanze, Landw. Versuchsst. 4 (1862) 318-340, and 5 (1863) 
116-136; Beitrage zur Pflanzencultur in wasserigen Nahrstoff Losungen. 
II. Ueber das Chlor als Pflanzennahrstoff, Landw. Versuchsst. 6 (1864) 
108-120. Nobbe, F., Ueber die physiologische Function des Chlor in der 
Pflanze, Landw. Versuchsst. 7 (1865) 371-386. Leydhecker, A., Ueber die 
physiologische Bedeutung des Chlor in der Buchweizenpflanze, Landw. 
Versuchsst. 8 (1866) 177-187. 
4 Beyer, A., Bericht liber die im Sommer 1867 an der Vei'suchs-Station 
Regenwalde ausgefiihrten Wasserculturversuche, Landw. Versuchsst. 11 
(1869) 262-287. 
6 Salm-Horstmar, Vers, und Resultate iib. d. Nahrung d. Pflanze. Braun- 
schweig (1856). 
