CULTURE OF PLANKTON DIATOM TIIALASSIOSIRA GRAVIDA CLEVE. 439 



3. The result appears to be due to some specific substance present in 



minute quantity in the natural sea-water which is essential to the 

 vigorous growth of the diatoms. The nature of this substance it 

 has not been possible to determine, but some evidence seems to 

 suggest that it is a somewhat stable organic compound. 



4. Provided the 1 per cent of natural sea-water is added, the various 



constituents of the artificial sea-water forming the basis of the 

 culture medium can be varied in amount within wide limits. The 

 sahnity of the medium can also be considerably altered without 

 serious detriment to the cultures. 



5. The experiments recorded are of interest as furnishing another instance 



of the importance in food substances of minute traces of particular 

 chemical compounds. They may also eventually throw Ught upon 

 the nature of the conditions in the sea which are specially favourable 

 to the production of plant life and therefore also of the animal life 

 which that plant life sustains. 



ADDENDUM. 



Since the above was printed a paper has been published by Prof. W. B. 

 Bottomley on " Some Accessory Factors in Plant Growth and Nutrition " 

 {Proceed. Roy. Soc, B., Vol. LXXXVIII, p.'237, Sept., 1914), in which it is 

 shown that a minute trace of an organic substance, which is formed by the 

 action of aerobic soil bacteria upon peat, acts as a powerful stimulant to 

 the growth of plants and of nitrogen-fixing bacteria. Following the 

 method of Cooper and Funk for obtaining " vitamines " from rice polish- 

 ings, namely, by precipitating by phosphotungstic acid from an aqueous 

 solution of the dry residue from an alcoholic extract, Bottomley has 

 succeeded in obtaining from the bacterized peat a substance which is 

 quite as powerful a stimulant to plant growth as the original alcoholic 

 extract of the bacterized peat. This substance, as in the case of Funk's 

 vitamines, can be further purified by precipitation with silver nitrate and 

 baryta, the resulting substance being an effective growth stimulant. 



